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postfix-users: Re: Problem with how postfix chooses MX'es

Re: Problem with how postfix chooses MX'es

From: Victor Duchovni <Victor.Duchovni_at_nospam>
Date: Mon Apr 11 2011 - 12:14:57 GMT
To: postfix-users@postfix.org

On Mon, Apr 11, 2011 at 02:06:51PM +0200, Administrator Systemu wrote:

> Hello all!
>
> I'm looking at logs of my postfix-2.6.6 and wonder how postfix chooses
> which MX it'll connect.

Random DNS order, as perturbed by demand-caching of sessions. Log parsers
should look at lines without "conn_use=<number>," when counting MX host
frequency, and should avoid counting multi-recipient messages as multiple
uses of the same MX.

> There is some "cool" configured domain simplusnet.pl:
>
> simplusnet.pl. 300 IN MX 10 mx1.plusnet.pl.
> simplusnet.pl. 300 IN MX 20 mx2.plusnet.pl.
> simplusnet.pl. 300 IN MX 50 mx3.plusnet.pl.

Mail deliveries will try mx1, but if that tempfails, mx2 or perhaps
mx3 may be tried in turn.

> mx1 & mx3 resolve to the same IP address, and permanently refuses
> connections to smtp port.
>
> Works only mx2. And now going back to logs:
>
> Apr 11 00:15:27 [postfix/smtp] 77ECE33058: to=<...@simplusnet.pl>,
> relay=none, delay=0.07, delays=0.06/0/0.02/0, dsn=4.4.1, status=deferred
> (connect to mx3.plusnet.pl[212.2.120.79]:25: Connection refused)

The connection to mx2 failed.

> Apr 11 00:24:37 [postfix/smtp] 77ECE33058: to=<...@simplusnet.pl>,
> relay=none, delay=550, delays=550/0.01/0.02/0, dsn=4.4.1, status=deferred
> (connect to mx3.plusnet.pl[212.2.120.79]:25: Connection refused)

The connection to mx2 failed...

> Apr 11 13:14:48 [postfix/smtp] 77ECE33058: to=<...@simplusnet.pl>,
> relay=mx2.plusnet.pl[212.2.120.80]:25, delay=46761,
> delays=46750/0.02/0.16/10, dsn=2.0.0, status=sent (250 OK
> id=1Q9F4n-0000Hj-LU)

Finally, after almost a day of trying, the connection to mx2 worked.

> Heh after 15 tries and 13 hours mail is delivered. Why postfix uses mx3 so
> many times?

Because mx2 is unreachable most of the time.

> And I have deliveries that not succeeded at all, because postfix was
> connecting only to mx3 till delivery expired.

This is not the case. You are not looing at all pertinent log entries.

-- Viktor.