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Co je 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.

Jak najít lidi k hovoru?

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.

Jaké výhody má Delta Chat vzhledem k ostatním četovacím systémům?

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.

Podporuje Delta Chat obrázky, videa a jiné přílohy?

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.

Kdo uvidí můj profilový obrázek?

Profilový obrázek není posílán s každou zprávou, ale dostatečně často k tomu aby tvé kontakty zvuobdrželi obrázek i když začnou používat nové zařízení.

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:

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

How do “Saved Messages” work?

Saved Messages is a chat that you can use to easily remember and find messages.

Messages stay saved even if they are edited or deleted - may it be by sender, by device cleanup or by disappearing messages of other chats.

What does the green dot mean?

You can sometimes see a green dot next to the avatar of a contact. It means they were recently seen in the last 10 minutes:

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 one of the above conditions are met.

Correct typos and delete messages after sending

While edited messages will have the word “Edited” next to the timestamp, deleted messages will be removed without a marker in the chat. Notifications are not sent and there is no time limit.

Note, that the original message may still be received by chat members who could have already replied, forwarded, saved, screenshotted or otherwise copied the message.

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).

Skupiny

Vytvoření skupiny

Přidat členy skupiny

Kdyź se nedopatřením odstraníš.

Nechci již přijímat zprávy ze skupiny.

What do the ticks shown beside outgoing messages mean?

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

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

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

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:

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:

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.

Note that the device token is encrypted between apps and notification proxy but it is not signed. The notification proxy thus never sees e-mail addresses, IP-addresses or any cryptographic identity information associated with a user’s device (token).

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?

Delta Chat uses a secure subset of the OpenPGP standard to provide automatic end-to-end encryption using these protocols:

Delta Chat does not query, publish or interact with any OpenPGP key servers.

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

All messages in Delta Chat are end-to-end encrypted by default. Since the Delta Chat Version 2 release series (July 2025) there are no lock or similar markers on end-to-end encrypted messages, anymore.

Can i still receive or send mails without end-to-end encryption?

If you use default chatmail relays, it is impossible to receive or send messages without end-to-end encryption.

If you instead create a profile using a classic e-mail server, you can send and receive messages without end-to-end encryption. Such messages lacking end-to-end encryption are marked with an e-mail icon email.

How can I establish a chat with a new contact?

You can send an invite link through another private chat, show an invitation QR code when next to each other or in a video call, or click on a “contact” that was shared in a chat.

Ask your chat partner to 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 end-to-end encryption is getting established.

Congratulations! You now will automatically use end-to-end encryption with this contact. If you add each other to chat groups, end-to-end encryption will be established among all members.

What does the green checkmark in a contact profile mean?

A contact profile might show a green checkmark green checkmark and an “Introduced by” line. 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 green-checkmarked contact to a group with only green-checkmarked members becomes an introducer. 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.

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.

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 requiring the whole message to be properly encrypted and signed. For example, “Detached signatures” are not treated as secure.

OpenPGP is not insecure by itself. Most publicly 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 and 2024.

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.

Are messages marked with the mail icon exposed on the Internet?

If you are sending or receiving e-mail messages without end-to-end encryption (using a classic e-mail server), they are still protected from cell or cable companies who can not read or modify your e-mail messages. But both your and your recipient’s e-mail providers may read, analyze or modify your messages, including any attachments.

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.

How does Delta Chat protect metadata in messages?

Unlike most other messengers, Delta Chat apps do not store any metadata about contacts or groups on servers, also not in encrypted form. Instead, all group metadata is end-to-end encrypted and stored on end-user devices, only.

E-mail Servers can therefore only see

All other message, contact and group metadata resides in the end-to-end encrypted part of messages.

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 relay to create chat profiles using random e-mail addresses for transport. 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 chat contacts using short-lived profiles can not be identified easily.

Does Delta Chat support “Sealed Sender”?

No, not yet.

The Signal messenger introduced “Sealed Sender” in 2018 to keep their server infrastructure ignorant of who is sending a message to a set of recipients. It is particularly important because the Signal server knows the mobile number of each account, which is usually associated with a passport identity.

Even if chatmail relays do not ask for any private data (including no phone numbers), it might still be worthwhile to protect relational metadata between addresses. We don’t foresee bigger problems in using random throw-away e-mail addresses for sealed sending but an implementation has not been agreed as a priority yet.

Does Delta Chat support Perfect Forward Secrecy?

No, not yet.

Delta Chat today doesn’t support Perfect Forward Secrecy (PFS). This means that if your 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 that Forward Secrecy only increases security if you delete messages. Otherwise, someone obtaining your decryption keys is typically also able to get all your non-deleted messages and doesn’t even need to decrypt any previously collected messages.

We designed a Forward Secrecy approach that withstood initial examination from some cryptographers and implementation experts but is pending a more formal write up to ascertain it reliably works in federated messaging and with multi-device usage, before it could be implemented in chatmail core, which would make it available in all chatmail clients.

Does Delta Chat support Post-Quantum-Cryptography?

No, not yet.

Delta Chat uses the Rust OpenPGP library rPGP which supports the latest IETF Post-Quantum-Cryptography OpenPGP draft. We aim to add PQC support in chatmail core after the draft is finalized at the IETF in collaboration with other OpenPGP implementers.

How can I manually 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.

Lze znovu použít můj stávající soukromý klíč?

No.

Delta Chat generates secure OpenPGP keys according to the Autocrypt specification 1.1. You can export your private key but you can not import additional private keys.

In general, we do not recommend or offer users to perform manual key management. We want to ensure that security audits can focus on a few proven cryptographic algorithms instead of the full breadth of possible algorithms allowed with OpenPGP.

Was Delta Chat independently audited for security vulnerabilities?

Yes, multiple times. The Delta Chat project continuously undergoes independent security audits and analysis, from most recent to older:

Více klientů najednou

Lze Delta Chat používat souběžně na více zařízeních?

Yes. You can use the same profile on different 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

Manual Transfer

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

Is Deletion, Pinning, Archiving, Saving, Muting etc. synced to all devices?

Yes.

If you e.g. delete a chat or a message from your phone, it will be deleted on your desktop as soon as it comes online again.

Notable exceptions are Delete old messages from Device, as different devices may have different storage capacities, and system specific settings as notification sounds.

Je v plánu vytvořit webovou verzi Delta Chatu?

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?

Where can I get webxdc apps?

How can I create my own webxdc apps?

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?

What are Broadcast Lists and how can I use them?

With a Broadcast List you can send a message to many recipients at once; the recipients cannot reply in that list. Broadcast lists are still highly experimental and will very probably be replaced by something else, stay tuned :)

How can I share my location with my chat partners?

Why can I choose to only watch the DeltaChat folder?

Toto je pokusné nastavení pro některé uživatele, kteří používají vlastní pravidla pro třídění e-mailu na serveru. Ne všichni poskytovatelé toto nabízí, ale někteří umožňují samočinně přesouvat všechny e-maily s hlavičkou “Chat-Version” do složky DeltaChat. To je něco co za běžných okolností dělá Delta Chat sám.

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

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?

Note: Changing email addresses is temporarily disabled because of ongoing changes to the DeltaChat core. It should be available again in a few months.

  1. 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.

  2. If possible, let your old e-mail provider forward all messages to your new address.

  3. 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.

Různé

Jaká oprávnění Delta Chat potřebuje?

Dle užívaného operačního systému můžeš být dotázán na udělení povolení této aplikaci. Zde je co Delta Chat dělá s těmito povoleními:

Pracuje Delta Chat s mým poskytovatelem e-mailu?

I want to manage my own server for Delta Chat. What do you recommend?

Proč musím Delta Chatu zadat mé e-mailové heslo? Je to bezpečné?

Podobně jako ostatní e-mailové programy, např. Thunderbird nebo Outlook, program potřebuje heslo k tomu aby mohl posílat e-maily. Samozřejmě, že heslo je uloženo pouze na tvém přístroji. Heslo je přenášeno pouze při přihlašení k e-mailovému serveru, který má i beztak přístup k tvým e-mailům.

Delta Chat má otevřený zdrojový kód, ze kterého lze ověřit, že program s osobními daty zachází bezpečně. Jsme rádi za každou odezvu, která udělá Delta Chat bezpečnější pro všechny.

Jaké zprávy Delta Chat zobrazuje?

By default, Delta Chat shows all e-mails.

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

Umí Delta Chat pracovat s e-maily v HTML?

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.

K čemu je dobré nastavení “Posílat si kopii”?

Posílat si kopii zpráv zaručuje, že zprávy se zobrazí na všech současně nastavených zařízeních. Pokud máš několik zařízení a nezapneš tuto funkci, uvidíš pouze příchozí zprávy, a zprávy odeslané jen z právě používaného přístroje. Ty odeslané z ostatních zařízení neuvidíš.

Kopie přijdou nejdříve do Příchozí složky, a pak jsou samočinně přesunuty do složky DeltaChat; ne do složky Odeslané. Do složky Odeslané se nepřesouvá nikdy nic. protože by to vyžadovalo přenášet zprávu dvakrát (jednou poslat přes SMTP, a jednou pro složku Odeslané přes IMAP).

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

Proč můžu nastavit sledování složky Odeslané?

Jediný důvod sledovat složku s odeslanými zprávami je používání jiného e-mailového programu (např. Thunderbird) spolu s Delta Chatem, a chtít z tohoto programu také psát zprávy do hovorů Delta Chatu.

Nicméně doporučujeme používat Delta Chat Desktop Client; ten lze stáhnout z get.delta.chat. Možnost sledování složky “Odeslané” může být v budoucnu zrušena. Byla totiž vytvořena v době, kdy Delta Chat Desktop nebyl dostupný na všech platformách.

Proč mohu zvolit nesledovat složku DeltaChat?

Někteří lidé užívají Delta Chat jako jediný e-mailový program, a chtějí užívat složku Příchozí / Inbox pro všechny zprávy i místo složky DeltaChat. Pokud zrušíš “Sleduj složku DeltaChat”, zruš také “přesouvat zprávy do složky DeltaChat”. Jinak hrozí, že mazání zpráv či nastavení na několika zařízeních nebude správně fungovat.

Lze Delta Chat používat s Proton Mail / Tutanota / Criptext?

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.

Mám zájem o technické podrobnosti. Kde najdu víc?

Where can my friends find Delta Chat?

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

Jak je financován vývoj Delta Chatu?

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 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 other contribution possibilities.