identify 143 vs 993 clients

[mj]

Hi,

I am trying to find a nice way to identify dovecot clients that are 
still configured to use port 143 to connect to our mailserver, from the 
dovecot logs.
I would then ask them to move over to 993, and finally disable port 143 
altogether.

When looking at the dovecot logs, it seems this is not logged in any 
obvious way.

Of course I could use netflow etc, but that would not give us usernames, 
but IP's, etc.

So, is there a nice way to somehow indicate in the dovecot logs, if a 
client connected on 143 or on 993?

Thanks!