[Dovecot] Mysql patch question

[Skye Poier]

Last question of the day I promise :)

If dovecot is configured to use the MySQL patch, ie:

auth_userdb = mysql /path/to/dovecot-mysql.conf
auth_passdb = mysql /path/to/dovecot-mysql.conf

Its not possible to "chain" authentication methods is it?
I mean, if its using MySQL it _cannot_ be configured to check passwd
(via "pam *") first, and then check mysql, right?

So, if I want to support real shell users (who are in /etc/passwd)
I will have to have them in mysql along with the "virtual" users.

......

OK I lied, one more question!

I love the feature that you can login with a username user at domain
and the domain is automatically parsed out.

Do these options have anything to do with the @domain part (referred to
as a realm in auth.txt) or are they for something else completely?  I'm
not sure what SASL is that it refers to in the example .conf

#auth_realms =
#auth_default_realm = 

Thanks,
Skye