[Dovecot] PAM problem with virtual domain/user ownership

[Mauricio Tavares]

	I am running dovecot 1.2.9 (ubuntu package, not from source) and wanted 
to use pam to authenticate my mail users who have no local accounts. 
I've done that before in an earlier release of dovecot and ubuntu, so I 
would not need to do set dovecot to ask LDAP directly.

So, I have in dovecot.conf:

# Authentication processes
mechanisms = plain login

passdb pam {
         args = "*"
}

userdb static {
           args = allow_all_users uid=virtual gid=virtual 
home=/var/spool/vmail/domain.com/%n
}

i.e. /var/spool/vmail/domain.com/ is owned by virtual:virtual,

drwxr-x--- 4 virtual virtual 4.0K 2011-01-23 11:45 domain.com

and that is how I would hope dovecot would be trying to login as. When I 
tried to login as user raub, the log file seems to tell me that it is 
trying to create /var/spool/vmail/domain.com/raub/cur as raub:users, not 
as virtual:virtual

Jan 22 06:35:02 mail dovecot: imap-login: Login: user=<raub>, 
method=PLAIN, rip=216.155.101.90, lip=216.155.101.94, TLS
Jan 22 06:35:02 mail dovecot: IMAP(raub): 
mkdir(/var/spool/vmail/domain.com/raub/cur) failed: Permission denied 
(euid=5016(raub) egid=100(users) missing +w perm: 
/var/spool/vmail/domain.com)

What am I missing here?