Kevin wrote:

I have just finished reading the info on the wiki on setting up virtual users with Dovecot and Postfix. http://wiki.dovecot.org/DovecotLDAPostfixAdminMySQL

I'm confused about the UID and GID's. In the docs it shows a user, vmail being created with a UID of 101. Then it looks like GID 12 is used for Postfix or Mail.

101 and 12 are just numbers. The fact that they are different shows that they can be different (and unless you enforce the numbers when creating the user and group, they will generally be different). There are generally more users than groups, so a new gid is generally lower than a new uid.

If your mailstore belongs to foo:bar (you did a 'chown foo:bar /path/to/mailtostore'), then set the uid to the uid of foo, and the gid to the gid of bar. the uid is found in /etc/passwd, the gid is found in /etc/group.

uid=grep "^foo" /etc/passwd |awk -F: '{print $3}' gid=grep "^bar" /etc/group |awk -F: '{print $3}'

a common setup is to use vmail:vmail as user:group (sometimes with uid=gid), but this doesn't change the above (the vmail use and the vmail group are two different beasts, because a user and a group are different concepts).

the choice of the group is dictated by access permissions that other programs (backup, retrain a spam filter, ....) need. It is recommended to make sure no other user (real or program) can access the mailstore unless it is really necessary, and if so, make sure this access cannot be subverted.