As an otherwise happy Evolution user, I was envious to Thunderbird users because of some of the plugins they have. One of the more useful ones is the Remove Duplicate Messages extension. A sane email client doesn’t create duplicates of course, but when you move mailboxes around, switch from an IMAP server to another, or restore mail from your backups after a disaster, it is easy to accidentally create hundreds of duplicates. (My recent return to Gmail since they started offering IMAP comes to mind!)
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