send/receive shows sending mail but nothing is in outbox

[fixitlane]

I am showing sending messages but there is nothing showing in the outbox.
When it is finished, nothing shows up in the sent box either. I then
sometimes get delivery failure notices for mails that I did not send.

 

[Brian Tillman]

I am showing sending messages but there is nothing showing in the
outbox. When it is finished, nothing shows up in the sent box either.
I then sometimes get delivery failure notices for mails that I did
not send.

Stuck read receipt, perhaps. See this:
http://www.howto-outlook.com/howto/deletereadreceipt.htm