I am still occasionally finding that an email has not been sent, but that it is sitting in the Outbox. I then stay in Outbox, but press Outbox’s “Send” button. But the email does not leave.
On several occasions recipients have told me they have received their emails although I have found those emails still apparently unmoved from my Outbox.
So there’s a problem with the Outbox clearing itself automatically whenever K-9 is online.
If an email in the Outbox has actually be sent, but is still showing in the Outbox, then when one presses “Send”, to move it, a message advising something like, “This message has already been sent” should appear.
I do not have an answer to your matter, but it is always best to include as much technical information as possible. What version of K-9 Mail are you using? What platform (smartphone, Chromebook, whatever), including version numbers? Have you tried generating a log? The more information available may help someone to assist you.
The Outbox problem described above occurs when using K-9 6.202, in Android 6.0.1, running on a Samsung tablet (Galaxy Tab SM-T700, Tab S 8.4).
A clue as to the cause of the problem could be the notification message: “Socket Time-out Exception”.
The same problem does not occur when I use K-9 6.202, in Android 12, on a Samsung smartphone (S10+).