Some e-mails are deleted

[ghost]

• Operating System (Linux/Mac/Windows/iOS/Android): Android 11
• Delta Chat Version: 1.28.1-fat
• Expected behavior: When I receive e-mails on Delta Chat they should not be deleted from the server, for no apparent reason.
• Actual behavior: Some e-mails are deleted for no apparent reason.
• Steps to reproduce the problem: I don't know how to reproduce it. All I know is that it's some e-mails sent by the bank 😅
• Screenshots:
• Logs: deltachat-log-20220224-123543.txt

[link2xt]

I see the bug.

Messages from your bank have no Message-ID. That's not a problem, DC generates a Message-ID for such messages normally. But here .unwrap_or_default() is used, so the message is treated as having a Message-ID equal to empty string: https://github.com/deltachat/deltachat-core-rust/blob/7c4a6ddcdf9c2b65c0148c2132cf21bd47073ace/src/imap.rs#L703

The result is that message is treated as duplicate of another message having empty message-ID and deleted.

DC should either not delete such messages or generate a Message-ID for them early if it's feasible.