>./imapgrab.py -d -v -f ~/user@email.com -s imap.mail.server -S -p 993 -u user@email.com -p password -m "_ALL_,-INBOX.Trash,-INBOX.Spam,-INBOX.Junk,-Trash,-Junk,-Spam"
I was moving mail from a Gmail account to a Gandi account about a year ago, before the recent spurt of development activity on Thunderbird.
Copy folders then?
Always copy, verify that the messages really are at the destination, then delete. I don't know why this isn't what Thunderbird does on its own when you move mail, but it isn't.
Thunderbird would start do it's things (moving emails for example) then freeze for a while and then all of a sudden stop in the middle of the operation complaining that it's a lot of work and asking me if I want to continue.
It's enraging every time. More so if you consider that IMAP is not transactional afaik.
The message IDs are mostly permanent, but the rfc says they can change so clients have to test them as per connection.
This means every time you check your mail with an IMAP client it's syncing some of the headers for every message.
getmail
Not sure how much work has been done on Thunderbird but I do an IMAP backup before archiving or making structural changes.
I should probably have an automated download for backup purposes set up ...