RoundCube webmail problem

[Self-Defence]

I've got a server running postfix witch receives mail fine since I can see emails being received in the /var/mail/username file. So I installed RoundCube webmail into witch I can login and even send email. But What I can't do is read recived emails.
I know that in order for RoundCube to be able to see emails the emails have to be in /home/username/mail but it's empty.
How do I get the mail from /var/mail/user to /home/user/mail and could Dovecot be the cause of this?

I almost forgot I tried the same installation but pointing it at another imap server and the darn thing worked the first time I loged in. So it probably is Dovecot right? I just have to figure out what's wrong with it.

Thanks for the help

[Self-Defence]

Well I figured out that it is Dovecot's fault. I tried connecting via imap with Thunderbird and got a Internal Error Occurred. And after checking every log I cluld think of I found this.

dovecot: imap(username): file_lock_dotlock() failed with mbox
 file /var/mail/username: Permission denied

So I went and checked the file permissions and ownership and everything was setup like it is on the other server whitch workes fine.

root@box:~# ls -l /var/mail/
total 1168
-rw------- 1 username   mail    2277 2007-06-19 17:17 username
-rw------- 1 user2 mail     754 2007-06-19 00:32 user2
-rw------- 1 user3 mail 1179790 2007-06-20 18:52 user3
root@box:~#

I just can't figure out what is going on.
Dovecot seems to be running since I tried to connect to it via telnet and got a reply.
Can anyone shed some light on my problem?

Thanks for the help.

[Self-Defence]

Well once again I've fixed the problem after a few days of bashing my head against the wall.
The solution is quite simple. I keept getting error messages "permission denied" so after crawling 5000 times over the dovecot.conf and reading I don't know how many sites the solution is add one line to the config:

mail_extra_groups = mail

Witch apparently gives dovecot permission to read anything in /var/mail/
Hope it helps someone else with a similar problem.

Now I've only got one problem now to fix. I can't seem to get RoundCube to work on a sub domain mail.mydomain.com it only works on an alias www.mydomain.com/webmail. I just can't seem to be able to login on the sub domain only on the top domain with the alias. Anyone have any ideas?

Thanks for the help and a good night to all.