Viktor Dukhovni:
Have you tried: strict_rfc821_envelopes = yes? There's nothing special about a "UTF-8 BOM" (there's no such thing in UTF-8 actually UTF-8 has no little-endian form). It is rather likely that your sender was not using SMTPUTF8, and so the encoding of non-ASCII envelopes is unspecified and use of such envelopes is invalid. Indeed your Dovecot LMTP service would likely equally object to any non-ASCII envelope.
I just tested it. With "strict_rfc821_envelopes = yes", and with a blank "smtpd_helo_restrictions" setting, email sent with the example SMTP script from my first message (wherein a UTF BOM is used in the email address in the MAIL FROM command) is accepted by Postfix.
Regarding, "UTF-8 BOM", I intentionally have only said "UTF BOM" thus far, because I understand what you're saying about UTF-8.
Indeed this behavior I'm talking about is without the client specifying SMTPUTF8.
I don't know if this behavior is specific only to a BOM. I just know that in my case, a BOM is what has caused my problem (bouncebacks for spam piling up in my queue, and backscatter).
