Can IMAP mail be migrated locally without loss of information?

Question

I need to save all of my IMAP mail in an account I have that will be expiring, to my local disk. The problem is that no matter which IMAP backup tool I can find, there is always some loss of information, like the "SEEN" flag, other metadata, or the folder structure of the e-mails. I need to preserve the status of whether a message was read or not -- the SEEN flag. This is apparently a design flaw with the IMAP protocol. Thunderbird's ImportExportTools has no way to save flags. Flags like SEEN are not naturally part of the message like all the other headers, and nearly no backup tools care about it. I once successfully used Imapsync to migrate one IMAP account on one server into a subfolder of this one which is on another server, but that's because it copies the flags into the server state. Imapsync is no longer free software, and I need to map the flags to local data this time. Ideally I would like to be able to open the messages locally in a program like Thunderbird and have it appear correctly and marked as read/unread, but at the very least I need to download the messages fully intact with all the metadata.

Is this at all possible?

Answer 1

OfflineIMAP can synchronize IMAP repositories to local Maildirs quite well. Preserving message state is part of its functionality.

(IMAP doesn't necessarily cause loss of the 'Seen' flag. Folders can be opened in read-only mode, and messages can be retrieved with BODY.PEEK without being marked.)

Answer 2

Have you tried IMAPSize yet? It is a freeware tool for Windows and suitable for backing up IMAP folders. I'm not exactly sure if it handles the seen flag correctly, but I think it's worth a try.