How do I temporarily suspend mail delivery to a specific domain (non-local) with Postfix?
Put messages in a HOLD state
/etc/postfix/main.cf:
smtpd_recipient_restrictions =
...
check_recipient_access hash:/etc/postfix/hold
/etc/postfix/hold:
gmail.com HOLD
blah.com HOLD
Make sure you run postmap hash:/etc/postfix/hold whenever you update the file.
If you want to release all messages on hold, use postsuper:
# postsuper -H ALL
You can do this with a transport map:
gmail.com defer: