Sry, talking to myself a bunch :-/ I changed
main.cf - address_verify_transport_maps = static:vpn:[back.mail01.example.com]:25 + address_verify_transport_maps = master.cf [mail01.example.com]:25 inet n - n - 1 postscreen -o smtpd_service_name=psint psint pass - - n - - smtpd + -o address_verify_transport_maps=static:vpn:[back.mail01.example.com]:25 ... and to initial test that seems to be working for address verification only at the postscreen instance. And no errors I can see. Yet. Now to wait for something to trigger one of those double-bounce messages. Jason