[Dovecot] understanding user_attrs and mail_uid/gid

Hello,

I'm trying to understand what's the difference between those parameters. In my dovecot.conf in the global section I have a definition of mail_uid and mail_gid. In my LDAP configuration used by passdb and userdb, I have a definition for user_attrs= uidNumber=500,gidNumber=8.

Here is a part of my configuration files (dovecot version: 2.1.7)

dovecot.conf

mail_gid = 8 mail_uid = 500

passdb { args = /etc/dovecot/dovecot-ldap.conf driver = ldap }

userdb { args = /etc/dovecot/dovecot-ldap.conf driver = ldap }

dovecot-ldap.conf

user_filter = (&(objectClass=posixAccount)(mailLocalAddress=%n)) user_attrs = uidNumber=500,gidNumber=8

So everything works fine when all those parameters are present in my configuration files. If I suppress one of them nothing is working (mail reading or delivering).

Can someone tell me where I can find a definition of those arguments, if found nothing relevant on the wiki.

Thanks,