I've been aggravated with SeaMonkey ever since I upgraded from the last legit version of Mozilla. First, there was the minor issue of it erasing/losing all of my email (5-6 years worth!) and since then, it's been slow as rocks and just not as stable a client as Mozilla. I miss Mozilla :-(.
My latest problem concerns email -- namely email sent via SMTP. The email downloads from my web server just fine, but when I respond and go to click "send", I get two error messages. Eventually I'm able to send the email by jumping through a couple of hoops, namely going back into account settings, switching between "Default" and "AT&T" SMTP servers (which is stupid, because in this case, they are one and the same) and then making sure no other email window is open. Once this is done, I can sometimes hit send and actually have the email go.
I've been checking all of my settings and passwords and ports, and I still haven't figured out what the issue is. I don't know whether the culprit is AT&T -- though they eventually let me send the email -- or SeaMonkey, or some combination of both. I'd like to like the blame for the whole mess on SeaMonkey's doorstep though. The fact if I shut down all email except the one I want to send tells me that it is most probably a software issue rather than AT&T being difficult. I'm trying to test another SMTP server, but that's causing me another load of problems.