Have tested using the ‘+’ delimiter with a Google mail account.
If I update /etc/postfix/check_recipient_access.cf to add in an e-mail address with a + in it. This should DISCARD the email as this check is done before the ‘+’ is processed. Use email ‘rwillett+drop AT example DOT com’.
Sent email ‘rwillett+drop AT example DOT com’ from Google mail and it is rejected - Pass
Sent email ‘willett+drop2 AT example DOT com’ from Google mail and it is correctly passed through the system - Pass
This appears to mean that the RECIPIENT_DELIMITER ‘+’ is honoured and still works with this proposed blocking system.
So far, so good. Item 3 on list appears to be OK.