Debugging SQL Statements from *any* client(s)

DEBUG5 is not enough to log SQL statements
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I've set up a courier-imap POP server authenticating against a
PostgreSQL table through authdaemond/authpgsqlrc. I can verify
courier-imap sends its SELECT statement to make a login attempt but
the POP login fails.

I know I'm pretty close to solve this but I have to see exactly how
the applied SELECT statement from courier-imap looks like. Since
debugging courier-imap is a pain, I've run postmaster with the highest
possible debug level but the SQL statements are not being logged yet
:-|

Any advice is very appreciated.