In your main.cf file on the inward-facing Postfix instance, add this:
transport_maps = hash:/etc/postfix/transport
In your /etc/postfix/transport file, add this:
office-domain.example.com smtp:offsite-server.example.com
Then run:
postmap /etc/postfix/transport
postfix reload
This should eliminate the delay, as postfix should ignore the MX records
and rely on its hardcoded transport information.
That's a weird configuration you've got there!
This archive was generated by hypermail 2.1.3 : Fri Aug 01 2014 - 16:25:27 EDT