[Dovecot] UID confusion

[Kevin]

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.

I'm not sure which it is and would like to know.

Bulldozer