This receiver side should be fixed and the fix should be released before we start protecting the Date header. Even if we decide that we don't want it (because of possibility of decryption failures and non-fully-downloaded message), receiver should support it.
While making PR #5715 I discovered that
Dateheader cannot be protected. If it is moved into protected part and removed from unprotected IMF header, mimeparser ignores it because it extracts theDateheader before decrypting the message: https://github.com/deltachat/deltachat-core-rust/blob/d40ec88b9458ea425b6a1ac04549daa5cae32554/src/mimeparser.rs#L223-L229This receiver side should be fixed and the fix should be released before we start protecting the
Dateheader. Even if we decide that we don't want it (because of possibility of decryption failures and non-fully-downloaded message), receiver should support it.