I am having a similar issue. I used to be able to send messages just fine.
Now they get hung in the Outbox. No error messages, they just don't go out
when I do a Send/Receive. I have found a clunky workaround. After I compose a
message and click Send, I immediately go to the Outbox. The icon for the
message shows an icon different from the "ready to send" icon. I highlight
the messagef, click Forward, edit the forwarding message to take out my extra
automatic signature at the top, then click Send. Now the message shows up
twice in the Outbox, one with each type of icon. I click Send/Receive, and
the one with the "ready to send" icon goes out. Then I delete the original
message that failed to send.
Can someone out there figure out why this behavior cropped up about two or
three weeks ago? It's really frustrating to have to treat every message this
way. I've run some of the latest Windows and Office Updates, which may have
introduced this issue. Does anyone have a guess about which one(s)?