Marking Emails as Junk Using IMAP4 Flags to Ensure Cross-Client Compatibility

[ngocnha]

I want to mark an email as junk using IMAP4 flags instead of automatically moving it to the default Junk folder on the server.
This way, email clients can either move it to their own Junk folder or keep it in the inbox based on the user's preference,
avoiding issues caused by differing default Junk folder names across various email clients.

[mdecimus]

Can you add this suggestion as a comment to #947 please?
I'm not sure all IMAP clients use the \Junk flag but for those who use it this is another way to trigger the spam classifier.