[exim] Non-verbose SQL errors

I'm using Postgresql for various Database lookups. If a database query
fails for whatever reason, the detailed SQL error message is shown to
the client during SMTP talk:

temporarily rejected RCPT <foo>: PGSQL: query failed: ERROR: duplicate key ...

Is it possible to change this to a more generic error message, e.g.
"internal database error"?

The detailed error message should be shown
a.) in the log file only
b.) only in debug-mode

Chris