> On Jul 29, 2019, at 1:29 PM, Дилян Палаузов <dilyan.palau...@aegee.org> wrote:
>
> SpamAssassin recomends inserting fake (lowest and highest) MX records
> https://cwiki.apache.org/confluence/display/spamassassin/OtherTricks to
> reduce Spam. E.g. MX aegee.org resolves to 90
> mxf-2.aegee.org. / 10 mail.aegee.org. / 1 mxf-1.aegee.org. and on
> mxf-1,2.aegee.org there is no SMTP server.
All sorts howtos recommend all sorts of cargo-cult advice, much of
worthless. This particular one is somewhat popular, but I'm aware
of any evidence of its efficacy. I prefer reliable, timely email
delivery.
> A mail has 3 recipients and is sent to a domain with fake MX records
> deployed, but otherwise has 50 distinct accepting
> IP addresses behind the MX records. The smtp server accepts one recipient
> per transaction and 451 defers the other
> recipients. Postfix picks up to 5 (smtp_mx_address_limit) distinct IP
> addresses from DNS. Postfix will connect first
> to the fake MX host.
No, because the guide recommends having no SMTP server at the fake
address, so that connection is refused, and Postfix immediately tries
the real MX host.
> Then postfix connects to two other hosts and each host consumes one
> recipient. Then postfix gives
> up and retries delivery to the last recipient later.
What is the origin this "one recipient" meme. Postfix sends
at most 50 by default, and the real MX is expected to accept
them all.
> Why doesn’t postfix handle the 4.5.3 status code in a special way? As long
> as per iteration the number of recipients
> is reduced, keep retrying without giving up.
Postfix strives to avoid tying up delivery agents on a single
message for too long, your strategy will too easily impose
unreasonable delays on delivery to other destinations.
If some site has a poorly thought out recipient limit of 1,
they suffer, not everyone else.
--
Viktor.
