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# Notes:
# D_REJECT and D_BOUNCE are similar, the difference is in who is responsible
# for informing the sender about non-delivery, and how informative
# the notification can be (amavisd-new knows more than MTA);
# With D_REJECT, MTA may reject original SMTP, or send DSN (delivery status
# notification, colloquially called 'bounce') - depending on MTA;
# Best suited for sendmail milter, especially for spam.
# With D_BOUNCE, amavisd-new (not MTA) sends DSN (can better explain the
# reason for mail non-delivery, but unable to reject the original
# SMTP session). Best suited to reporting viruses, and for Postfix
# and other dual-MTA setups, which can't reject original client SMTP
# session, as the mail has already been enqueued.