The box is still running PostgreSQL 8.1 and this started to increase a few weeks ago. It is only happening while the server is a bit busy.
fatal: pgsql:/etc/postfix/pgsql/relay_domains.cf(0,lock|fold_fix): table lookup problem
fatal: pgsql:/etc/postfix/pgsql/relay_domains.cf(0,lock|fold_fix): table lookup problem
fatal: pgsql:/etc/postfix/pgsql/relay_domains.cf(0,lock|fold_fix): table lookup problem
No other changes where made, so it seems to be related to a load increase. A new upgrade Debian Jessie box is in the works, but is there anything I can do in the meantime?