Viktor Dukhovni:
However, right below that is: http://www.postfix.org/postconf.5.html#strict_smtputf8which will do the job.
Thank you, Victor. That setting indeed allows me to reject Unicode characters (and not just BOMs) in a MAIL FROM command, when SMTPUTF8 isn't specified, as I initially requested.
However, unrelated then to Postfix behavior, it highlights the real root of my problem, which isn't even solved by my PCRE check (unless I ban all Unicode), and that's that Dovecot doesn't have proper SMTPUTF8 support. Postfix verifies the RCPT TO address with Dovecot LMTP, Postfix ends the session with the client, indicating success, Postfix sends the message onto Dovecot LMTP, and Dovecot LMTP generates a bounce. The solution would then be to make Dovecot not bounce Unicode MAIL FROM addresses, so I'll pursue that angle. Thanks again.
