Is anyone here having problems sending emails using Thunderbird?

I have been using 1.5.10 with no problems up until about a week and a half ago, when suddenly it started to have difficulty sending emails, needing several retries before successfully sending.
Now it will not send at all, but will still receive just fine.

I have checked all the obvious things like SMTP settings, password caps lock etc., tried turning off anti-virus and firewall, but nothing makes a difference.

I don't seem to be the only one with this problem either:

http://forums.mozillazine.org/viewtopic.php?t=546933

http://forums.mozillazine.org/viewtopic.php?t=547156

Maybe a Windows update has borked something?
_________________________
Peter.

"I spent 90% of my money on women, drink and fast cars. The rest I wasted." - George Best