Just had a bit of a weird problem with Thunderbird v3.0.3 throwing an error dialog with the following text:
An error occurred while sending mail. The mail server responded: qq write error or disk full (#4.3.0). Please check the message and try again.
Or in image form:
This of course looks like a server error, so I panicked and harassed our Ops guys, thinking the mail server was running out of space. Some simple testing indicated this wasn’t the problem – I was able to send through our mail server’s web interface (Zimbra) and others were able to receive mail with no problems, so it was clearly a problem at my end.
I restarted Thunderbird with no effect, and rebooted with no effect.
The solution was to right click my ‘Sent’ mail folder and hit ‘Rebuild Index’. I guess the index got corrupted somehow and it couldn’t write to the Sent mail folder, triggering that (wrong) error message.