I have some email messages without a Date header accessible in an IMAP mailbox. This results in incorrect behaviour of the MUA (Mozilla Thunderbird). I expected this to be violating RFCs, but maybe it isn't. To prevent incorrect mail data, which occurs on every initial sync, I intend to fix this.
The MUA has an extension, with which headers of a message can be edited manually. However, what it really does, is creating a new message and deleting the old one.
Is there a method to modify a message via IMAP or in another way generally?
How could I use that method, without manually talking to the server.
No. IMAP messages are immutable, by definition. If they were not, nothing would know whether they needed to resync them or not.
From RFC 3501, 2.3.1.1, statement 4:
- The combination of mailbox name, UIDVALIDITY, and UID must refer to a single immutable message on that server forever. In particular, the internal date, [RFC-2822] size, envelope, body structure, and message texts (RFC822, RFC822.HEADER, RFC822.TEXT, and all BODY[...] fetch data items) must never change. This does not include message numbers, nor does it include attributes that can be set by a STORE command (e.g., FLAGS).