Detect port number of SASL AUTH request?

[MRob]

Hi, this is partly Postfix related, but I want to know if there could be 
way to distinguish port of the SASL AUTH request to segregate user 
services.

Currently I use unix listener for dovecot sasl auth, but could change to 
inet_listener.

Only way I can think is to have different SASL AUTH services for each 
master.cf entry where its needed. But is it possible for Dovecot to have 
more than one SASL AUTH services with different configuration setup? It 
would be nicer if there was a way for Postfix to tell Dovecot about the 
port the client connected on.

Or maybe it can be done with a SASL realm? I'm not sure how? Any help 
please?