Why do sent messages remain in my Apple Mail “Drafts” folder after being sent?

We’ve occasionally received reports of message copies remaining in the “Drafts” folder after being successfully sent with Apple Mail. This seems more likely to happen with large messages that have attachments.

This is due to a bug in Apple Mail, and is not related to our servers. People complain about it happening with other servers, too, such as this report and this one.

Nobody’s mentioned this problem with other IMAP mail programs such as the excellent Mozilla Thunderbird, so it’s something outside of our control, unfortunately. Hopefully Apple will eventually fix it, although the problem has existed for years.