$ ls -l /var/spool/mail
lrwxrwxrwx 1 root root 7 Feb 14 2012 /var/spool/mail -> ../mail
As displayed, my /var/spool/mail
is just a symlink back to /var/mail
. I didn't create that but if you don't have it, and it's causing you significant grief in Thunderbird, I wouldn't hesitate to add a link:
sudo ln -s '../mail' /var/spool/mail
And now I read the original answer, it does suggest to use /var/mail/username
and shows a screenshot of how to specify it (in the Server Settings tab).
If you're getting read errors and /var/spool/mail
exists check:
file /var/spool/mail
to make sure it's the right thing
stat /var/mail/$USER
is it accessibly by your current user? Is it owned by the right person? Have you copied this from a filesystem with different UID/GIDs? If in doubt, reset the permissions back to the correct ones:
sudo chown $USER:mail /var/mail/$USER
chmod 0600 /var/mail/$USER