There are tools such as imapsync, mailsync, etc, which are very useful if you're backing up a remote host which runs IMAP. I've certainly exported/synced from

There are tools such as imapsync, mailsync, etc, which are very useful if you're backing up a remote host which runs IMAP. I've certainly exported/synced from gmail, gmx, and similar commercial providers to local Maildir archives.