Časté dotazy

Co je Delta Chat?

Delta Chat je nový četovací messenger, který posílá zprávy přes e-mail, pokud možno zašifrované metodou Autocrypt. Netřeba žádného nového účtu. Pro Delta Chat prostě použijete ten, který už máte pro svůj e-mail.

Jak najít lidi k hovoru?

Delta Chatem můžete napsat na jakýkoli e-mail i v případě, že příjemce Delta Chat nepoužívá. Není nutné aby příjemce instaloval stejnou aplikaci jako vy, jak vyžadují ostatní četovací systémy.

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?

Podporuje Delta Chat obrázky, videa a jiné přílohy?

How can I add or switch between multiple accounts?

Tap the profile image in the upper left corner to switch accounts. You will also find Add Account there.

You may also wish to learn how to add accounts to 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 Signature Text/Status/Motto with Delta Chat?

Yes, you can do so under “Settings > Profile > Signature Text”. Your contacts who use Delta Chat will see it when they view your contact details. To everyone else, It will appear as an e-mail signature below the text of all your messages.

What do Pinning, Muting and Archiving mean?

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

To archive or pin a chat, long tap (Android), use the chat’s menu (Android/Desktop) or swipe to the left (iOS); to mute a chat, use the chat’s menu (Android/Desktop) or the chat’s profile (iOS).

What does the green dot mean?

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).


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”?

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 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 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?

Meet your chat partner outside Delta Chat, preferably in person but a second channel like a video chat or a different messenger is fine as well. Perform the following QR show/scan procedure with your chat partner. One of you is the “Inviter”, the other is the “Joiner”.

Inviter side:

Joiner side:

If the QR code scanning doesn’t work in your situation, you can also Share (or Copy to Clipboard) an equivalent invite link to the other person through a second channel.

Both Inviter and Joiner:

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

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 green checkmark 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 green checkmark 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 account 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 account from the new device and rather import the backup file to re-create their account. 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?


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:

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 Delta Chat optimized e-mail server instance to create pseudonymous temporary accounts through QR-code scans. Note that Delta Chat apps on all platforms support multiple accounts so you can easily use action-specific “1-week” or “1-month” accounts next to your “main” account with the knowledge that all temporary account data, along with all metadata, will be deleted. Moreover, if a device is seized then contacts using temporary e-mail accounts 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 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.

Lze znovu použít můj stávající soukromý klíč?

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.

Nemohu do Delta Chatu zavést můj stávající PGP klíč.

Nejpravděpodobnější příčinou jsou zašifrované klíče, nebo klíče s heslem. Takové klíče Delta Chat nepodporuje.  Můžeš odstranit šifrování nebo heslo a zkusit to znovu. Pokud je potřeba použít zaheslovaný klíč vytvoř / použij zástupnou adresua a pak přidej nový Delta Chat účet s tímto klíčem.

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

Delta Chat podporuje běžné formáty OpenPGP klíčů, nicméně neočekáváme, že soukromé klíče ze všech aplikací budou fungovat. To není cíl, a ve skutečnosti věttšina nových uživatelů Delta Chatu nemá žádný stávající klíč. Přesto se snažíme podporovat soukromé klíče z co nejvíce možných zdrojů.

Odstranění hesla ze soukromého klíče závisí na programu ze kterého PGP klíč pochází. Enigmail umí nastavit prázdnou hodnotu hesla v okně Key Management. U GnuPG lze to samé nastavit z příkazové řádky. Pro ostatní programy by mělo jít nalézt řešení na Interentu.

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:

Více klientů najednou

Lze Delta Chat používat souběžně na více zařízeních?

Yes. Delta Chat 1.36 comes with a new, experimental function for using the same account 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.


Manual Transfer

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

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?

How can I share my location with my chat partners?

What does the experimental database encryption actually protect?

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 change my account to a different e-mail address?

  1. Change your address in “Settings → Advanced → Password and Account” and enter the password of your new 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.


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 e-mail 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.

Poskytovatelé e-mailu s podporou OAuth2, např. “gmail.com” či “yandex.ru”, nepotřebují při přihlašování tvé heslo. V takovém případě je uložen pouze vygenerovaný přístupový kód.

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.

Je hovor v Delta Chatu skutečně interaktivní, když užívá E-Mail?

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 Protonmail / Tutanota / Criptext?

How can I delete my account?

As you use an e-mail account for Delta Chat, how you can delete your account depends on your e-mail provider. We don’t have any control over your e-mail account, so unfortunately we can’t help you with that.

If you want to keep the account, but uninstall Delta Chat, it is recommended to leave any group chat before uninstalling Delta Chat.

Mám zájem o technické podrobnosti. Kde najdu víc?

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:

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.