Nondetectable version [protocol cloaking against censors, hide Chat-Version]

[alexey-aleksey]

Some countries block messengers by removing packets related to specific protocol. I need the version that sends e-mails without whatever data specific for Delata.Chat
Such version can have 2 billions of potential users in China, Russian Federation, Iran, etc.
So ability to look like usual e-mail can be more important than features supported by specific custom fields in headers, etc.

Expected behavior

No way to detect that letter was sent from Delta.chat

Actual behavior

Custom fields in headers like “Chat-Version”, “Chat-Group”, “Autocrypt” , etc.

Example Images

[ian]

Partial answer:

Identify Deltachat messages by header

In any case, I think if someone decides to censor email, they will just filter out encrypted mails rather than DC mails.

Hide group emails from data mining

solved! Delta Chat now uses the header To: hidden-recipients by default. this, and most other metadata are removed by implementing, RFC 9788, “Header Protection for Cryptographically Protected Email”, kind of successor of the mentioned “memoryhole”. the following blog post gives a higher-level and broader overview about things that work in email in 2026, but are kind of unexpected to many

It won't take off with email interoperability issues

This is not a bug, the real To is protected with RFC 9788: Header Protection for Cryptographically Protected Email It is inside the encrypted part. The real list of the recipients that the server uses is in the RCPT TO SMTP commands which are not part of the message. This is similar to how Bcc works. It is not clear what you tested in each case. E.g. with “DC (Fastmail) → Gmail” I assume you typed in the email address of the recipient? I don’t understand what “but reply isn’t available in DC”…

Headers malformed?

The autocrypt header went in the encrypted section as of 2.25: Android: Delta Chat v2.25.0 released with improved channels! What you’re seeing is not a malformed header, it’s how a normal email is formatted: the headers, 2 newlines, then the body. --something is a part separator to split between the different parts in the body, it’s expected

Related:

Document the minimum requirements necessary for chatmail interoperability

I am currently working on Delta Chat interoperability for bower/notmuch ( GitHub - wangp/bower: A curses terminal client for the Notmuch email system · GitHub , https://notmuchmail.org). My goal is to support enough of the features Delta Chat uses that I can comfortably use my command line email setup to exchange messages with Delta Chat users. Currently, I am also using my command line setup in Multi Device Mode together with the Delta Chat Android app from F-Droid. A couple of days back, I ra…

Name (and describe) the Header Confidentiality Policy used by Delta Chat [RFC 9788]

RFC 9788 “Header Protection for Cryptographically Protected Email” includes the following statement: The authors of this document hope that implementers with deployment experience will document their chosen HCP and the rationale behind their choice. The Header Confidentiality Policy used by Delta Chat is easy enough to describe. In RFC 9788-style pseudocode, it might look like this: hcp_unnamed(name, val_in) -> val_out: if lower(name) is 'from': assert that val_in is an RFC 5322…

More thorough solution:

Disguise ciphertext to avoid email provider censor abnormal behavior

The U.S. will ban China’s IM app WeChat in the near future. Due to the existence of the Great Firewall (GFW) of China, millions of Chinese in the United States are facing the dilemma of losing contact with their Chinese families. Reuters : WeChat U.S. ban cuts off users link to families in China But there are few alternatives for them, because of the following 2 reasons: All well-known IM app outside of China, such as Telgram, Signal, WhatsApp, are blocked by the GFW, so family members can…

[alexey-aleksey]

@ian

Partial answer:

Do you mean that Delta-specific fields are hidden inside the encrypted header ?

[ian]

The referenced comments describe that most are already migrated except Chat-Version

However, as it’s already mentioned there, you will be trivially blocked based on visibly using encryption in the first place, so you will actually need steganography, shaped cover traffic and mix networks implemented on top of email to succeed on the long run.