HowtoForge still comes in handy. This is one of those times:

mailq | awk 'BEGIN { RS = "" } / falko@example\.com$/ { print $1 }' | tr -d '*!' | postsuper -d -

File under “what to do when postfix goes berserk”.

Unless you set local_recipient_maps to nothing, just so:

local_recipient_maps =
luser_relay = some@address.com


Postfix will ignore the luser_relay setting and winge at you.

Documentation is tucked away at the bottom of the page here.