Outgoing messages get stuck in outbox sent failure, what could be causing this error?

[AC Question]

Outgoing messages get stuck in outbox sent failure

I keep getting a sending failed message and the outgoing message just stays in my out box.

 

[Crashdamage]

Re: Outgoing messages get stuck in outbox sent failure

If it happens only sometimes and not with all email all the time, then the most likely cause is you did no have a working internet connection when you tried to send.
What is the error message you see?