Preguntes freqüents

Què és Delta Chat?
Groups
Instant message delivery and Push Notifications
Encryption and Security
Multi-client
webxdc apps
Experimental Features
Miscellaneous

Què és Delta Chat?

Delta Chat is a reliable, decentralized and secure messaging app, available for mobile and desktop platforms.

Delta Chat feels like Whatsapp or Telegram but you can also use and regard it as an e-mail app. You can signup anonymously to a variety of interoperable chatmail servers which are minimal e-mail servers optimized for fast and secure operations. Or you may use classic e-mail servers and an existing e-mail account in which case Delta Chat acts as an e-mail app.

Com puc trobar gent amb qui xatejar?

To securely setup contact with others scan an invite QR code or share an invite link. This is required when using a (default) chatmail-based chat profile because chatmail servers reject un-encrypted outgoing messages.

If you create a chat profile with a classic e-mail address you may manually create a contact if you know their e-mail address and then write a message to them even if the recipient is not using Delta Chat.

Quins són els avantatges de Delta Chat comparat amb altres missatgers?

Anonymous chat profiles with fast, secure and interoperable chatmail servers which offer instant Push Notifications for iOS and Android devices.
Pervasive multi-profile and multi-device support on all platforms.
Interactive web apps in chats for gaming and collaboration
Audited end-to-end encryption safe against network and server attacks.
Free and Open Source software, both app and server side. Built on E-mail and Web Internet Standards, to avoid “yet another standard syndrome (xkcd 927)”

What if I expect a message from someone I didn’t write to in the past?

If a message comes from an unknown contact, it appears as a request. You need to accept the request before you can reply.
You can also “delete” it if you don’t want to chat with them for now. This does not delete the message on the server, only on your device. So you can still deal with the message in a different mail app.
If you delete a request, future messages from that contact will still appear as message request, so you can change your mind. If you really don’t want to receive messages from this person, consider blocking them.

Does Delta Chat support images, videos and other attachments?

Yes. Beside the plain text, all e-mail attachments are displayed as separate messages. Outgoing messages get attachments as needed automatically.
For performance, images are optimized and sent at a smaller size by default, but you can send it as a “file” to preserve the original.

What are profiles? How can I switch between them?

A profile is a name, a picture and some additional information for encrypting messages. A profile lives on your device(s) only and uses a chatmail or a classic e-mail server to transport messages.

On first installation of Delta Chat a first profile is created.

Later, you can tap your profile image in the upper left corner to Add Profiles or to Switch Profiles.

You may want to use separate profiles for political, family or work related activities, or e. g. for a dedicated “spam-profile” with which you register at websites and platforms that tend to cause unsolicited messages (“spam”) sooner or later.

You may also wish to learn how to use the same profile on multiple devices.

Who sees my profile picture?

You can add a profile picture in your settings. If you write to your contacts or add them via QR code, they automatically see it as your profile picture.
Contacts who don’t use Delta Chat do not see the profile picture (however, of course, they can install Delta Chat :)
For privacy reasons, no one sees your profile picture until you write a message to them.
Your profile picture isn’t sent with every message, but regularly enough that your contacts will re-receive your profile picture, even if they add a new device.

Can I set a Bio/Signature/Status/Motto with Delta Chat?

Yes, you can do so under Settings → Profile → Bio. Your contacts who use Delta Chat will see it when they view your contact details. Moreover, it will appear as a classic e-mail signature.

What do Pinning, Muting and Archiving mean?

Use these tools to organize your chats and keep everything in its place:

Pinned chats always stay atop of the chat list. You can use them to access your most loved chats quickly or temporarily to not forget about things.
Mute chats if you do not want to get notifications for them. Muted chats stay in place and you can also pin a muted chat.
Archive chats if you do not want to see them in your chat list any longer. Archived chats remain accessible above the chat list or via search.
When an archived chat gets a new message, unless muted, it will pop out of the archive and back into your chat list. Muted chats stay archived until you unarchive them manually.

To use the functions, long tap or right click a chat in the chat list.

What does the green dot mean?

Since Delta Chat 1.34 you can sometimes see a “green dot” next to the avatar of a contact. It means they were “recently seen”.
In detail: it means, that in the last 10 minutes, Delta Chat has seen them:
- either because they messaged you directly,
- because they wrote something to a group you are both a member of,
- because they sent you a read receipt for a message you wrote,
- or because they sent data to your Delta Chat app by using a webxdc app.
So this is not a real time online status - and if someone doesn’t answer right away even though they seem to be online, don’t worry and give them some space ;-)
On the other hand, others will not always “see that you are online”. If you have turned off read receipts, they will not see the green dot until you message them or write to a group they’re in as well.

How do disappearing messages work?

You can turn on “disappearing messages” in the settings of a chat, at the top right of the chat window, by selecting a time span between 1 minute and 5 weeks.

Until the setting is turned off again, each chat member’s Delta Chat app takes care of deleting the messages after the selected time span. The time span begins when the receiver first sees the message in Delta Chat. The messages are deleted both in each email account on the server, and in the app itself.

Note that you can rely on disappearing messages only as long as you trust your chat partners; malicious chat partners can take photos, or otherwise save, copy or forward messages before deletion.

Apart from that, if one chat partner uninstalls Delta Chat, the messages will not get deleted from their email account. They will most likely also not be decryptable anymore (as long as they were encrypted in the first place).

Groups

Creation of a group

Select New chat and then New group from the menu in the upper right corner or hit the corresponding button on Android/iOS.
On the following screen, select the group members and define a group name. You can also select a group avatar.
As soon as you write the first message in the group, all members are informed about the new group and can answer in the group (as long as you do not write a message in the group the group is invisible to the members).

Add members to a group

Cada membre del grup te els mateixos drets que els altres. Per això mateix, tothom pot esborrar a qualsevol membre o afegir-ne de nous.
Per afegir o esborrar membres, prem a sobre del nom del grup des de la finestra de xat.

I have deleted myself by accident.

As you’re no longer a group member, you cannot add yourself again. However, no problem, just ask any other group member in a normal chat to re-add you.

I do not want to receive the messages of a group any longer.

Either delete yourself from the member list or delete the whole chat. If you want to join the group again later on, ask another group member to add you again.
As an alternative, you can also “Mute” a group - doing so means you get all messages and can still write, but are no longer notified of any new messages.

What do the ticks shown beside outgoing messages mean?

One tick means that the message was sent successfully to your provider.
Two ticks mean that at least one recipient’s device reported back to having received the message.
Recipients may have disabled read-receipts, so even if you see only one tick, the message may have been read.
The other way round, two ticks do not automatically mean that a human has read or understood the message ;)

What happens if I turn on “Delete old messages from server”?

By default, Delta Chat stores all messages locally on your device. If you e.g. want to save storage space at your mail provider, you can configure Delta Chat to delete old already-received messages on the server automatically. They still remain on your device until you delete them there, too.
To turn it on, go to Delete Old Messages → Delete Messages from Server in the “Chats and Media” settings. You can set a timeframe between “At once” and “After 1 year”. All e-mails received by Delta Chat will be deleted from the server after this timeframe.
Note that if you use Delta Chat on more than one device, you need to leave the message on the server with a sufficient timeframe so that the other device(s) can download them, too.

What happens if I turn on “Delete old messages from device”?

If you want to save storage on your device, you can choose to delete old messages automatically.
To turn it on, go to “delete old messages from device” in the “Chats & Media” settings. You can set a timeframe between “after an hour” and “after a year”; this way, all messages will be deleted from your device as soon as they are older than that.

Instant message delivery and Push Notifications

What are Push Notifications? How can I get instant message delivery?

Push Notifications are sent by Apple and Google “Push services” to a user’s device so that an inactive Delta Chat app can fetch messages in the background and show notifications on a user’s phone if needed.

Push Notifications work with all chatmail servers on

iOS devices, by integrating with Apple Push services.
Android devices, by integrating with the Google FCM Push service, including on devices that use microG instead of proprietary Google code on the phone.

As of May 2024, classic e-mail servers do not support Push Notifications for Delta Chat users.

Are Push Notifications enabled on iOS devices? Is there an alternative?

Yes, Delta Chat automatically uses Push Notifications for chatmail profiles. And no, there is no alternative on Apple’s phones to achieve instant message delivery because Apple devices do not allow Delta Chat to fetch data in the background. Push notifications are automatically activated for iOS users because Delta Chat’s privacy-preserving Push Notification system does not expose data to Apple that it doesn’t already have.

Are Push notifications enabled / needed on Android devices?

If a “Push Service” is available, Delta Chat enables Push Notifications to achieve instant message delivery for all chatmail users. If you are using a classic e-mail provider instead of chatmail servers, Push Notifications are not available.

In the Delta Chat “Notifications” settings for “Instant delivery” you can change the following settings effecting all chat profiles:

Use Background Connection: If you are not using a Push service, you may disable “battery optimizations” for Delta Chat, allowing it to fetch messages in the background. However, there could be delays from minutes to hours. Some Android vendors even restrict apps completely (see dontkillmyapp.com) and Delta Chat might not show incoming messages until you manually open the app again.
Force Background Connection: This is the fallback option if the previous options are not available or do not achieve “instant delivery”. Enabling it causes a permanent notification on your phone which may sometimes be “minified” with recent Android phones.

Both “Background Connection” options are energy-efficient and safe to try if you experience messages arrive only with long delays.

How private are Delta Chat Push Notifications?

Delta Chat Push Notification support avoids leakage of private information. It does not leak e-mail, IP address or message content (not even encrypted) to any system involved in the delivery of Push Notifications.

Here is how Delta Chat apps perform Push Notification delivery:

A Delta Chat app obtains a “device token” locally and stores it on the chatmail server.
When a chatmail server receives an e-mail for a Delta Chat user it forwards the “device token” to the central Delta Chat notification proxy.
The central Delta Chat notification proxy forwards the “device token” to the respective Push service (Apple, Google, etc.), without ever knowing the IP or e-mail address of Delta Chat users.
The central Push Service (Apple, Google, etc.) wakes up the Delta Chat app on your device to check for new messages in the background. It does not know about the chatmail or e-mail address of the device it wakes up. The central Apple/Google Push services never see an e-mail address (sender or receiver) and also never see any message content (also not in encrypted forms).

As of May 2024, chatmail servers know about “device tokens” but we plan to encrypt this information to the notification proxy such that the chatmail server never learns the device token.

The central Delta Chat notification proxy is small and fully implemented in Rust and forgets about device-tokens as soon as Apple/Google/etc processed them, usually in a matter of milliseconds.

Resulting from this overall privacy design, even the seizure of a chatmail server, or the full seizure of the central Delta Chat notification proxy would not reveal private information that Push services do not already have.

Why does Delta Chat integrate with centralized proprietary Apple/Google push services?

Delta Chat is a free and open source decentralized messenger with free server choice, but we want users to reliably experience “instant delivery” of messages, like they experience from Whatsapp, Signal or Telegram apps, without asking questions up-front that are more suited to expert users or developers.

Note that Delta Chat has a small and privacy-preserving Push Notification system that achieves “instant delivery” of messages for all chatmail servers including a potential one you might setup yourself without our permission. Welcome to the power of the interoperable and massive chatmail and e-mail system :)

Encryption and Security

Which standards are used for end-to-end encryption?

Autocrypt is used for automatically establishing end-to-end encryption with contacts and group chats. Autocrypt uses a limited and secure subset of the OpenPGP standard. End-to-End encrypted messages are marked with a padlock .

Secure-Join protocols are used for establishing chats with guaranteed end-to-end encryption which protects against network attacks and compromised servers. Chats marked with a green checkmark guarantee end-to-end encrypted messages.

How can i know if messages are end-to-end encrypted?

All end-to-end encrypted messages carry a padlock:

padlock in bubble

End-to-end encryption is guaranteed if there is a green checkmark next to the chat title:

green checkmark in title

How can I get guaranteed end-to-end encryption and green checkmarks?

If you have a second communication channel with your chat partner, like a video chat or a different messenger, you can generate an invite link.

If you are together in person, you can show a QR code to your chat partner.

For Group invitations, tap the chat group title to see its member list, and select “QR Invite code”.
For direct 1:1 chat invitations, tap the QR Code icon on the Delta Chat app main screen.

Let your chat partner scan the QR image with their Delta Chat app, or click “Copy” or “Share” to create an invite link and share it with your chat partner.

Now wait while Secure-Join network messages are exchanged between both devices.

If both devices are online, both sides will eventually see a (group or direct) chat with a green checkmark next to the title.
If one of the devices is offline, the green checkmarks will only appear later when the device is internet-connected again and the Secure-Join network protocol completed.

Congratulations! You now will automatically use guaranteed end-to-end encryption with this contact and both of you can add each other to green-checkmarked groups green checkmark , thereby automatically spreading guaranteed end-to-end encryption among its members.

What does the green checkmark and “guaranteed end-to-end encryption” mean?

Chat titles with green checkmarks mean that all messages in the chat will be end-to-end encrypted and can not be read or altered by compromised e-mail servers or Internet providers. Joining green-checkmarked group chats safely spreads everybody’s encryption information (and green checkmarks) in a manner that guarantees end-to-end encryption in the group and among members.

Contact profiles with green checkmarks mean that messaging a contact is currently guaranteed to be end-to-end encrypted. Every green-checkmarked contact either did a direct QR-scan with you or was introduced by a another green-checkmarked contact. Introductions happen automatically when adding members to groups. Whoever adds a contact to a green-checkmarked group becomes an introducer to those members who didn’t yet know about the added contact. In a contact profile you can tap on the “Introduced by …” text repeatedly until you get to the one with whom you directly did a QR-scan.

Note that in a contact profile you may see and tap introducers but there is no green checkmark in the profile title. This usually means that the contact “sent a message from another device”.

For more in-depth discussion of “guaranteed end-to-end encryption” please see Secure-Join protocols and specifically read about “Verified Groups”, the technical term of what is called here “green-checkmarked” or “guaranteed end-to-end encrypted” chats.

A contact “sent a message from another device”, what can i do?

Your chat with a contact lost guaranteed end-to-end encryption. The green checkmark was removed for this chat and contact when you see this warning. If you find the sudden drop of guaranteed end-to-end encryption surprising for this contact then don’t accept the warning! Instead check with your contact through a second channel like a video call, other messenger or a phone call, to find out what happened.

If your contact actually caused the drop of guaranteed end-to-end encryption please see the next paragraphs for common reasons and their mitigations. Regardless, all other green-checkmarked chats remain guaranteed end-to-end encrypted even if the contact is a member there.

Your contact is using Delta Chat on a second device (phone or laptop)

If they have another device with a Delta Chat app running, they should remove the profile from the new device and add it as a second device as described here. As soon as they message you afterwards, the warning will be gone and guaranteed encryption is established with both devices of your contact.

Your contact reinstalled Delta Chat using their old account login

If they have a backup file, they should remove the profile from the new device and rather import the backup file to re-create their profile. As soon as they message you afterwards, the warning will be gone and guaranteed encryption is re-established for this contact.

If they don’t have a backup file, it’s best to perform a QR scan with your chat partner to re-establish guaranteed end-to-end encryption.

Your contact sent a mail through a webmail interface or another e-mail app and will get back to using Delta Chat soon again.

If you are sure that the contact sometimes uses webmail, or another mail app lacking end-to-end encryption, then you may accept the warning. As soon as your contact uses Delta Chat again, guaranteed end-to-end encryption will be automatically re-established.

Your contact stopped using Delta Chat entirely

Sometimes remaining in contact is more important than end-to-end encryption. “Transport Layer Encryption” (TLS) may still meaningfully protect the confidentiality of your messages between your device and the e-mail server. But without end-to-end encryption you and your contact are trusting your e-mail server to not read or manipulate your messages, and to not hand them to third parties.

In any case, you can not do much else than accept the warning. Please also remove the contact from any active green-checkmarked group which you can find in “Shared chats” in the Contact profile. This spares your contact from getting “unreadable” messages.

If the contact removed Delta Chat because of buggy or undesirable behaviour, please consider posting to our support forum to help us identify and address common problems. Thanks!

Are attachments (pictures, files, audio etc.) end-to-end encrypted?

Yes.

When we talk about an “end-to-end encrypted message” we always mean a whole message is encrypted, including all the attachments and attachment metadata such as filenames.

Is OpenPGP secure?

Yes, Delta Chat uses a secure subset of OpenPGP and only displays a padlock security indicator on a message if the whole message is properly encrypted and signed. For example, “Detached signatures” are not treated as secure.

OpenPGP is not insecure by itself. Most publically discussed OpenPGP security problems actually stem from bad usability or bad implementations of tools or apps (or both). It is particularly important to distinguish between OpenPGP, the IETF encryption standard, and GnuPG (GPG), a command line tool implementing OpenPGP. Many public critiques of OpenPGP actually discuss GnuPG which Delta Chat has never used. Delta Chat rather uses the OpenPGP Rust implementation rPGP, available as an independent “pgp” package, and security-audited in 2019.

We aim, along with other OpenPGP implementors, to further improve security characteristics by implementing the new IETF OpenPGP Crypto-Refresh which was thankfully adopted in summer 2023.

Did you consider using alternatives to OpenPGP for end-to-end -encryption?

Yes, we are following efforts like MLS or Saltpack but adopting them would mean breaking end-to-end encryption interoperability with all other e-mail apps that typically support OpenPGP encryption. So it would not be a light decision to take and there must be tangible improvements for users.

Delta Chat takes a holistic “usable security” approach and works with a wide range of activist groupings as well as renowned researchers such as TeamUSEC to improve actual user outcomes against security threats. The wire protocol and standard for establishing end-to-end encryption is only one part of “user outcomes”, see also our answers to device-seizure and message-metadata questions.

Is Delta Chat vulnerable to EFAIL?

No, Delta Chat never was vulnerable to EFAIL because its OpenPGP implementation rPGP uses Modification Detection Code when encrypting messages and returns an error if the Modification Detection Code is incorrect.

Delta Chat also never was vulnerable to the “Direct Exfiltration” EFAIL attack because it only decrypts multipart/encrypted messages which contain exactly one encrypted and signed part, as defined by the Autocrypt Level 1 specification.

Is a message exposed in cleartext if end-to-end encryption is not available?

Even if your messages are not guaranteed to be end-to-end encrypted, they are still protected from Internet providers like cell or cable companies. However, your and your recipient’s e-mail providers may read, analyze or even modify your messages, including any attachments, if they are not end-to-end encrypted.

Delta Chat by default uses strict TLS encryption which secures connections between your device and your e-mail provider. All of Delta Chat’s TLS-handling has been independently security audited. Moreover, the connection between your and the recipient’s e-mail provider will typically be transport-encrypted as well. If the involved e-mail servers support MTA-STS then transport encryption will be enforced between e-mail providers in which case Delta Chat communications will never be exposed in cleartext to the Internet even if the message was not end-to-end encrypted.

Note that maintaining guaranteed end-to-end encryption on top of TLS encryption provides pervasive safety between your and the recipient’s devices. Not even your e-mail or Internet provider will be able to read or modify your messages.

How does Delta Chat protect metadata in messages?

Delta Chat protects most message metadata by putting the following information into the end-to-end encrypted part of messages:

Subject line
Group avatar and name
MDN (read receipt) requests (Chat-Disposition-Notification-To)
Disappearing message timer (Ephemeral-Timer)
Chat-Group-Member-Removed, Chat-Group-Member-Added
Secure-Join header containing secure join commands
Notification about enabling location streaming
WebRTC room URL

E-Mail servers do not get access to this protected metadata but they do see the message date as well as the message size, and, more importantly, the sender and receiver addresses. E-mail servers need receiver addresses to route and deliver messages to recipient’s devices.

How to protect metadata and contacts when a device is seized?

Both for protecting against metadata-collecting e-mail servers as well as against the threat of device seizure we recommend to use a chatmail server to create pseudonymous temporary profiles through QR-code scans. Note that Delta Chat apps on all platforms support multiple profiles so you can easily use situation-specific profiles next to your “main” profile with the knowledge that all their data, along with all metadata, will be deleted. Moreover, if a device is seized then contacts using temporary profiles can not be identified easily, as compared to messengers which reveal phone numbers in chat groups which in turn are often associated with legal identities.

How can i check encryption information?

You may check the end-to-end encryption status manually in the “Encryption” dialog (user profile on Android/iOS or right-click a user’s chat-list item on desktop). Delta Chat shows two fingerprints there. If the same fingerprints appear on your own and your contact’s device, the connection is safe.

How can I check the encryption status of messages?

A little padlock in a message bubble denotes that the message was properly end-to-end encrypted from the given sender. If there is no padlock, the message was not properly end-to-end encrypted most likely because the sender uses an app or webmail interface without support for end-to-end–encryption.

Why do I see unencrypted messages?

If a contact uses a non-Autocrypt e-mail app, all messages involving this contact (in a group or 1:1 chat) will not be end-to-end encrypted, and thus not show a “padlock” with messages. Note that even if your contacts use Delta Chat on their account, they might also use a non-Autocrypt e-mail app on that account which then may cause intermittently unencrypted messages. Replying unencrypted to unencrypted messages is mandated by Autocrypt to prevent unreadable messages on the side of your contacts and their non-Autocrypt e-mail app.

How can i get an end-to-end encrypted chat with a Delta Chat contact who sometimes uses webmail or another non-Autocrypt e-mail app?

If you need a safely end-to-end encrypted chat with a contact who is using their e-mail account both with Delta Chat and non-Autocrypt apps (e.g. webmail), it’s best to setup guaranteed end-to-end encryption with them and then create a guaranteed end-to-end encrypted group chat with you two as members. In this group chat all messages will be end-to-end encrypted even if the direct chat between you two has a “… sent a message from another device” warning.

How can I ensure message end-to-end encryption and deletion?

The best way to ensure every message is end-to-end encrypted, and metadata deleted as quickly as possible is using chats with guaranteed end-to-end encryption and turning on disappearing messages.

Guaranteed end-to-end encrypted chats protect against MITM attacks and turning on disappearing messages deletes the messages on the server after a user-configured time.

If you don’t need a longer-lived copy of your messages on the server, you can also turn on “delete messages from server automatically”.

Does Delta Chat support Perfect Forward Secrecy?

No, Delta Chat doesn’t support Perfect Forward Secrecy (PFS). This means that if your Delta Chat private decryption key is leaked, and someone has collected your prior in-transit messages, they will be able to decrypt and read them using the leaked decryption key.

Note, however, that if anyone obtains to your decryption keys, they will typically also be able to obtain your messages, irrespective if Perfect Forward Secrecy is in place or not. The typical real-world situation for leaked decryption keys is device seizure which we discuss in our answer on metadata and device seizure.

It is possible that Delta Chat evolves to support Perfect Forward Secrecy, because OpenPGP is just a container for encrypted messages but encryption key management (and thus key rotation or key “ratcheting”) could be organized in flexible ways. See Seqouia’s PFS prototype for existing experiments in the OpenPGP implementor community.

Is end-to-end encryption of Delta Chat as safe as Signal?

It depends on what is important to you. Delta Chat does not support PFS like Signal does but it provides guaranteed end-to-end encrypted chats that are safe against compromised servers or corrupted networks. Signal and most other PFS-supporting messengers do not provide a practical scheme for protecting chat groups from network attacks which are arguably more worrysome than a potential attacker who seizes your phone and private encryption setup but somehow not your messages, yet has a full record of all past encrypted messages.

In any case, Delta Chat’s end-to-end encryption uses a secure subset of OpenPGP which has been independently security-audited.

Can I reuse my existing private key?

Yes. The best way is to send an Autocrypt Setup Message from the other e-mail client. Look for something like Start Autocrypt Setup Transfer in the settings of the other client and follow the instructions shown there.

Alternatively, you can import the key manually in “Settings -> Advanced settings -> Import secret keys”. Caution: Make sure the key is not protected by a password, or remove the password beforehand.

If you don’t have a key or don’t even know you would need one - don’t worry: Delta Chat generates keys as needed, you don’t have to hit a button for it.

I can’t import my existing PGP key into Delta Chat.

The most likely cause is that your key is encrypted and/or uses a password. Such keys are not supported by Delta Chat. You could remove the passphrase encryption and the password and try the import again.

Another common error is having the wrong file ending. Use the ASCII armored format and an .asc file ending.

Delta Chat supports common OpenPGP private key formats, however, it is unlikely that private keys from all sources will be fully supported. This is not the main goal of Delta Chat. In fact, the majority of new users will not have any key prior to using Delta Chat. We do, however, try to support private keys from as many sources as possible.

Removing the password from the private key will depend on the software you use to manage your PGP keys. With Enigmail, you can set your password to an empty value in the Key Management window. With GnuPG you can set it via the command line. For other programs, you should be able to find a solution online.

Was Delta Chat independently audited for security vulnerabilities?

The Delta Chat project underwent four independent security audits and one independent security analysis, from most recent to older:

2024 March, we received a deep security analysis from the Applied Cryptography research group at ETH Zuerich and addressed all raised issues. See our blog post about Hardening Guaranteed End-to-End encryption for more detailed information and the Cryptographic Analysis of Delta Chat research paper published afterwards.
2023 April, we fixed security and privacy issues with the “web apps shared in a chat” feature, related to failures of sandboxing especially with Chromium. We subsequently got an independent security audit from Cure53 and all issues found were fixed in the 1.36 app series released in April 2023. See here for the full background story on end-to-end security in the web.
2023 March, Cure53 analyzed both the transport encryption of Delta Chat’s network connections and a reproducible mail server setup as recommended on this site. You can read more about the audit on our blog or read the full report here.
2020, Include Security analyzed Delta Chat’s Rust core, IMAP, SMTP, and TLS libraries. It did not find any critical or high-severity issues. The report raised a few medium-severity weaknesses - they are no threat to Delta Chat users on their own because they depend on the environment in which Delta Chat is used. For usability and compatibility reasons, we can not mitigate all of them and decided to provide security recommendations to threatened users. You can read the full report here.
2019, Include Security analyzed Delta Chat’s PGP and RSA libraries. It found no critical issues, but two high-severity issues that we subsequently fixed. It also revealed one medium-severity and some less severe issues, but there was no way to exploit these vulnerabilities in the Delta Chat implementation. Some of them we nevertheless fixed since the audit was concluded. You can read the full report here.

Multi-client

Can I use Delta Chat on multiple devices at the same time?

Yes. Delta Chat 1.36 comes with a new, experimental function for using the same profile on different devices:

Make sure both devices are on the same Wi-Fi or network
On the first device, go to Settings → Add Second Device, unlock the screen if needed and wait a moment until a QR code is shown
On the second device, install Delta Chat
On the second device, start Delta Chat, select Add as Second Device, and scan the QR code from the old device
Transfer should start after a few seconds and during transfer both devices will show the progress. Wait until it is finished on both devices.

In contrast to many other messengers, after successful transfer, both devices are completely independent. One device is not needed for the other to work.

Troubleshooting

Double-check both devices are in the same Wi-Fi or network
On Windows, go to Control Panel / Network and Internet and make sure, Private Network is selected as “Network profile type” (after transfer, you can change back to the original value)
On iOS, make sure “System Settings / Apps / Delta Chat / Local Network” access is granted
On macOS, enable “System Settings / Privacy & Security / Local Network / Delta Chat”
Your system might have a “personal firewall”, which is known to cause problems (especially on Windows). Disable the personal firewall for Delta Chat on both ends and try again
Guest Networks may not allow devices to communicate with each other. If possible, use a non-guest network.
Ensure there is enough storage on the destination device
If transfer started, make sure, the devices stay active and do not fall asleep. Do not exit Delta Chat. (we try hard to make the app work in background, but systems tend to kill apps, unfortunately)
Delta Chat is already logged in on the destination device? You can use multiple profiles per device, just add another profile
If you still have problems or if you cannot scan a QR code try the manual transfer described below

Manual Transfer

This method is only recommended if “Add Second Device” as described above does not work.

On the old device, go to “Settings -> Chats and media -> Export Backup”. Enter your screen unlock PIN, pattern, or password. Then you can click on “Start Backup”. This saves the backup file to your device. Now you have to transfer it to the other device somehow.
On the new device, in the “I already have a profile” menu, choose “restore from backup”. After import, your conversations, encryption keys, and media should be copied to the new device.
- If you use iOS: and you encounter difficulties, maybe this guide will help you.
You are now synchronized, and can use both devices for sending and receiving end-to-end encrypted messages with your communication partners.

Are there any plans for introducing a Delta Chat Web Client?

There are no immediate plans but some preliminary thoughts.
There are 2-3 avenues for introducing a Delta Chat Web Client, but all are significant work. For now, we focus on getting stable releases into all app stores (Google Play/iOS/Windows/macOS/Linux repositories) as native apps.
If you need a Web Client, because you are not allowed to install software on the computer you work with, you can use the portable Windows Desktop Client, or the AppImage for Linux. You can find them on get.delta.chat.

webxdc apps

In Delta Chat, you can share webxdc apps, attachments with an .xdc file extension. They can do very different things, and make Delta Chat a truly extendable messenger.

How private are webxdc apps?

webxdc apps can not send data to the Internet, or download anything.
A webxdc app can only exchange data within a Delta Chat chat, with its copies on the devices of your chat partners. Other than that, it’s completely isolated from the Internet.
The privacy a webxdc app offers is the privacy of your chat - as long as you trust the people you chat with, you can trust the webxdc app as well.
This also means: it can be a privacy risk to open webxdc apps in chats where you don’t trust the members - as you know it from e-mail attachments, where you only open attachments from senders you trust, and not from spammers.

Where can I get webxdc apps?

In general, anyone can share webxdc apps with each other without restrictions.
From webxdc.org/apps.
You can send ‘hi’ to xstore@testrun.org to see an experimental webxdc appstore. All of the apps are open source and for free.
Many people write their own webxdc apps and post them to the Delta Chat forum.

How can I create my own webxdc apps?

webxdc apps are just zip files containing html, css, and javascript code.
You can extend the Hello World example app to get started.
All else you need to know is written in the documentation.
If you have question, you can ask others with experience in the Delta Chat Forum.

Experimental Features

We are very grateful for feedback on these features - do you want to share your ideas? Join the Forum to contribute. You may conveniently login via Delta Chat and a QR code scan, another rather stable experiment we run on the side (sic!).

How can I use audio/video calls with Delta Chat?

To turn on audio/video calls, go to the “experimental features” section in the advanced settings and choose a “Video Chat Instance”.
When you invite others to a video chat, it is opened in your browser/app at once. The others receive an e-mail with a link to the video chat. This way, it is also compatible if your chat partners don’t use Delta Chat.
Note that there is no ring tone on the other side, and your chat partners will not get interrupted by a video chat invite.
You can use any video chat service which allows joining by link. Just add the link in the settings.
For example, to use the flagship Jitsi Meet instance, you could enter https://meet.jit.si/$ROOM. The $ROOM variable will be a random value; this way, you will have a new random jitsi room every time you call someone.

What are Broadcast Lists and how can I use them?

With a Broadcast List you can send a message to many recipents at once; when they reply to you, you get the reply in your direct 1:1 chat with them. The recipients can’t see each other.
Technically, it is an E-Mail with many recipients in BCC.
You can turn on the feature in the “experimental features” section in the advanced settings. Then you can create a Broadcast List from the “New Chat” dialog.
In case you are using more than one device, Broadcast Lists are currently not synced between them.
Messages sent to broadcast lists are not encrypted. Encryption would break anonymity, because then all recipients would know who else received it (Sending individual mails to everyone would be worse for rate limit and network consumption reason).

You can turn on location streaming in the “experimental features” section of the advanced settings.
Now, if you want to share your location in a chat, go to “attach” and select “location”. You can now set a time frame in which your location will be streamed to your chat partners, between 5 minutes and 6 hours.
When your location changes, the others in the chat can view it on a map in the chat.
To see the map and view locations of others, you need to turn on the feature in the advanced settings.
This feature will not share your location with anyone except your chat partners. Map tiles are downloaded from OpenStreetMap.
On desktop, the OS typically can’t determine your location. Instead you can right click on the map and describe a location, which is sent to the chat as a message, but also appears on the map.

Why can I choose to only watch the DeltaChat folder?

This is an experimental setting for some people who are experimenting with server-side rules. Not all providers support this, but with some you can move all mails with a “Chat-Version” header to the DeltaChat folder. Normally, this would be done by the Delta Chat app.

Enabling “Only Fetch from DeltaChat folder” makes sense if you have both:

enabled a server-side rule to move all messages with Chat-Version header to the DeltaChat folder, and
have set the “Show classic emails” setting to “no, chats only”.

In this case, Delta Chat doesn’t need to watch the Inbox, and it’s enough to only watch the DeltaChat folder.

How can I use a different e-mail address with my profile?

Change your address in “Settings → Advanced → Password and Account” and enter the password of your new e-mail account (and if necessary, server settings). You will get an information notice about the fact that you are moving to a new address. An additional notice will also show up in your “Device messages” chat.
If possible, let your old e-mail provider forward all messages to your new address.
Tell your contacts that you changed your address. Writing to guaranteed end-to-end encrypted chats and groups, will make them notice your move automatically and they will continue chatting with you using your new address.

Note that Delta Chat will not retrieve messages anymore from your old e-mail provider. If you didn’t configure your e-mail provider to forward messages (step 2.) only those contacts to whom you sent a message in a guaranteed end-to-end encrypted chat will send messages to your new address.

To learn more about this the details behind this, read our blogpost on it.

Miscellaneous

Which permissions does Delta Chat need?

Depending on the operating system in use, you may be asked to grant permissions to the app. This is what Delta Chat does with these permissions:

Camera (can be disallowed)
- take pictures and videos: for sending Photos
Contacts (can be disallowed)
- read your contacts: to discover contacts to chat with
Location (can be disallowed)
- access approximate location (network location sources): for the location streaming feature
- access precise location (GPS and network location sources): for the location streaming feature
Microphone (can be disallowed)
- record audio: for audio messages
Storage (can be disallowed)
- modify or delete the contents of your SD card: to download message attachments
- read the contents of your SD card: to share files with your contacts
Other app capabilities
- change your audio settings: so you can choose ring tones and volume for notifications and audio messages
- run at startup: so you don’t have to start Delta Chat manually
- control vibration: for notifications
- view network connections: to connect to your E-Mail provider
- prevent phone from sleeping: so you can easier copy the security code during the Autocrypt Setup Message
- have full network access: to connect to your E-Mail provider
- view Wi-Fi connections: to connect to your E-Mail provider
- ask to ignore battery optimisations: for achieving “instant message delivery”

Does Delta Chat work with my e-mail-provider?

With a rather good chance: Yes :)
However, some providers need special options to work properly, see Provider Overview

Most mail servers will work well. But what we personally recommend is a combination of mailcow and mailadm, as described in this blogpost.
You can find an installation guide on our website.

Why do I have to enter my E-Mail password into Delta Chat? Is this secure?

As with other E-Mail programs like Thunderbird, K9-Mail, or Outlook, the program needs the password so you can use it to send and receive mails. Of course, the password is stored only on your device. The password is only transmitted to your E-Mail provider (when you login), which has access to your mails anyway.

As Delta Chat is Open Source, you can check the Source Code if you want to verify that your credentials are handled securely. We are happy about feedback which makes the app more secure for all of our users.

Which messages do appear in Delta Chat?

By default, Delta Chat shows all e-mails.

At “Settings → Advanced → Show Classic E-Mails”, you can change this. You have these options:

“No, chats only”: Only messages sent by other Delta Chat users and replies to your Delta Chat messages are shown. This makes most sense if you use the same e-mail account for normal e-mails as well.
“All”: Delta Chat shows all e-mails that are sent to your email address. This makes sense if you want to use Delta Chat for all your e-mails, so no message gets lost. This is the default setting.
“For accepted contacts”: Delta Chat shows all e-mails from contacts with whom you already have a chat, but new chats only pop up for Delta Chat messages. This helps to decide on a case-by-case basis whether you want to have a conversation in Delta Chat or in a “normal” e-mail app.

Does Delta Chat support HTML e-mails?

Yes, incoming HTML messages come with a “Show full message” button. Outgoing messages always use plain text.

Can I set the E-Mail Subject with Delta Chat?

Delta Chat sets (and encrypts!) the classic e-mail subject automatically to the group name or to the sender name.

So if you want to set the subject yourself, for example for a formal e-mail to a business contact, you can create a group with only yourself and the recipient(s). Set the Chat Title to the Subject you want, and then send your e-mail as the first message. If the recipients don’t use Delta Chat, it will look like a normal, formal e-mail to them. You will get bonus professionalism points if you set a signature text.

What is the “Send Copy to Self” setting good for?

Sending a copy of your messages to yourself ensures that you receive your own messages on all devices. If you have multiple devices and don’t turn it on, you see only the messages from other people, and the messages you send from the current device.

The copy is sent to the Inbox, and then moved to the DeltaChat folder; it’s not put into the “Sent” folder. Delta Chat never uploads anything to the Sent folder because this would mean uploading a message twice (once through SMTP, and once through IMAP to Sent folder).

The default setting for “Send Copy to Self” is “on”.

Why can I choose to watch the “Sent” folder?

The only reason one wants to watch the Sent folder is if you are using another mail program (like Thunderbird) next to your Delta Chat app, and want your MUA to participate in chat conversations.

However, we recommend using the Delta Chat Desktop Client; you can download it on get.delta.chat. The option to watch the “Sent” folder might go away in the future. It was introduced at a time where there was no Delta Chat Desktop client available on all platforms.

Why can I choose not to watch the DeltaChat folder?

Some people use Delta Chat as a regular email client, and want to use the Inbox folder for their mail, instead of the DeltaChat folder. If you disable “Watch DeltaChat folder”, you should also disable “move chat messages to DeltaChat”. Otherwise, deleting messages or multi-device setups might not work properly.

Is Delta Chat compatible with Protonmail / Tutanota / Criptext?

Yes and No.
No, you can not use your Protonmail, Tutanota, or Criptext account with Delta Chat; they do not offer receiving mails via IMAP.
In any case you can use Delta Chat to send Messages to people who use Protonmail, Tutanota, or Criptext. Those messages will not be end-to-end encrypted, though. The end-to-end encryption those providers offer is not compatible with Autocrypt, the standard Delta Chat uses.
Delta Chat can end-to-end-encrypt through any e-mail provider with any Autocrypt-enabled e-mail app.

How can I delete my account?

If you use a default chat profile you can simply uninstall the app. This will automatically trigger deletion of all associated account data on the chatmail server. For more info, please refer to nine.testrun.org account-deletion for the default onboarding server, or the respective page from your chosen 3rd party chatmail server.

If you have set up your chat profile on multiple devices you need to remove it from all devices.

If you are using more than one account, but don’t want to get rid of all of them, you can remove it in the account switcher menu (on android and iOS), or in the sidebar with a right click (in the desktop client).

Accounts on classic e-mail providers will not be deleted automatically; how you can delete your account depends on your e-mail provider. We don’t have any control over e-mail accounts at those providers, so unfortunately we can’t help you with that.

If you want to continue using a classic e-mail account with other apps, but uninstall Delta Chat, it is recommended to leave any group chat before uninstalling Delta Chat. Otherwise you might receive undecryptable messages from those group chats.

I’m interested in the technical details. Can you tell me more?

See Standards used in Delta Chat.

Where can my friends find Delta Chat?

Delta Chat is available for all major and some minor platforms:

The official website, https://delta.chat/download shows all options in detail
If unavailable, use the mirror at https://deltachat.github.io/deltachat-pages
Open one of the following app stores and search for “Delta Chat”: Google Play Store, F-Droid, Huawei App Gallery, Amazon App Store, iOS and macOS App Store, Microsoft Store
Check the package manager of your Linux distributions
Android APKs are also available on https://github.com/deltachat/deltachat-android/releases

How are Delta Chat developments funded?

Delta Chat does not receive any Venture Capital and is not indebted, and under no pressure to produce huge profits, or to sell users and their friends and family to advertisers (or worse). We rather use public funding sources, so far from EU and US origins, to help our efforts in instigating a decentralized and diverse chat messaging eco-system based on Free and Open-Source community developments.

Concretely, Delta Chat developments have so far been funded from these sources, ordered chronologically:

The NEXTLEAP EU project funded the research and implementation of verified groups and setup contact protocols in 2017 and 2018 and also helped to integrate end-to-end Encryption through Autocrypt.
The Open Technology Fund gave us a first 2018/2019 grant (~$200K) during which we majorly improved the Android app and released a first Desktop app beta version, and which moreover moored our feature developments in UX research in human rights contexts, see our concluding Needfinding and UX report. The second 2019/2020 grant (~$300K) helped us to release Delta/iOS versions, to convert our core library to Rust, and to provide new features for all platforms.
The NLnet foundation granted in 2019/2020 EUR 46K for completing Rust/Python bindings and instigating a Chat-bot eco-system.
In 2021 we received further EU funding for two Next-Generation-Internet proposals, namely for EPPD - e-mail provider portability directory (~97K EUR) and AEAP - email address porting (~90K EUR) which resulted in better multi-profile support, improved QR-code contact and group setups and many networking improvements on all platforms.
From End 2021 till March 2023 we received Internet Freedom funding (500K USD) from the U.S. Bureau of Democracy, Human Rights and Labor (DRL). This funding supported our long-running goals to make Delta Chat more usable and compatible with a wide range of e-mail servers world-wide, and more resilient and secure in places often affected by internet censorship and shutdowns.
2023-2024 we successfully completed the OTF-funded Secure Chatmail project, allowing us to introduce guaranteed encryption, creating a chatmail server network and providing “instant onboarding” in all apps released from April 2024 on.
In 2023 and 2024 we got accepted in the Next Generation Internet (NGI) program for our work in webxdc PUSH, along with collaboration partners working on webxdc evolve, webxdc XMPP, DeltaTouch and DeltaTauri. All of these projects are partially completed or to be completed in early 2025.
Sometimes we receive one-time donations from private individuals. For example, in 2021 a generous individual bank-wired us 4K EUR with the subject “keep up the good developments!”. 💜 We use such money to fund development gatherings or to care for ad-hoc expenses that can not easily be predicted for, or reimbursed from, public funding grants. Receiving more donations also helps us to become more independent and long-term viable as a contributor community.

Donate Money
Last but by far not least, several pro-bono experts and enthusiasts contributed and contribute to Delta Chat developments without receiving money, or only small amounts. Without them, Delta Chat would not be where it is today, not even close.

The monetary funding mentioned above is mostly organized by merlinux GmbH in Freiburg (Germany), and is distributed to more than a dozen contributors world-wide.

Please see Delta Chat Contribution channels for both monetary and and other contribution possibilities.