I’ve read in the manual that importing IMAP mail is not currently supported. However looking at the Library files I can see the folder structure of the IMAP account replicated with a bunch of emlx files that seem to be the emails (I set up Mail to cache everything). Could I import those directly?
Another possibility would be to create a local mailbox of things I want to import and move the messages from the IMAP account to this mailbox, hoping the MailTags information is preserved. Would you recommend such an approach?