postfix uses A record for MX less domains

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postfix uses A record for MX less domains

Mario Theodoridis
Hi everyone,

i'm having a curious issue with our postfix instance.

It seems it is sending emails to a domain's A record when no MX is found.

Is that standard? If so, can i disable this somewhere?

connect to bikinibottom.com[208.73.211.70]:25: Connection refused
to=<[hidden email]>, relay=none, delay=407,
delays=407/0.01/0.15/0, dsn=4.4.1, status=deferred (connect to
bikinibottom.com[208.73.211.70]:25: Connection refused)

# dig mx bikinibottom.com
;bikinibottom.com.              IN MX

# dig a bikinibottom.com
bikinibottom.com.       300     IN      A       208.73.211.70


It's a temporary failure on top of that, left to linger in the queue til....

Clue sticks would be appreciated.

--
Mit Freundlichen Grüßen / Regards

Mario Theodoridis

regify GmbH
Römerstrasse 39 | D-78183 Hüfingen
Amtsgericht Freiburg HRB 709343
Telefon: +49 771 8978 4238

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Re: postfix uses A record for MX less domains

Ralf Hildebrandt-2
* Mario Theodoridis <[hidden email]>:
> Hi everyone,
>
> i'm having a curious issue with our postfix instance.
>
> It seems it is sending emails to a domain's A record when no MX is found.
>
> Is that standard?

Yes.

> If so, can i disable this somewhere?

No.

> connect to bikinibottom.com[208.73.211.70]:25: Connection refused
> to=<[hidden email]>, relay=none, delay=407,
> delays=407/0.01/0.15/0, dsn=4.4.1, status=deferred (connect to
> bikinibottom.com[208.73.211.70]:25: Connection refused)

transport_maps:

bikinibottom.com error:This domain does not accept mail

--
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Re: postfix uses A record for MX less domains

Mario Theodoridis
On 31/03/17 15:01, Ralf Hildebrandt wrote:

> * Mario Theodoridis <[hidden email]>:
>> Hi everyone,
>>
>> i'm having a curious issue with our postfix instance.
>>
>> It seems it is sending emails to a domain's A record when no MX is found.
>>
>> Is that standard?
>
> Yes.
>
>> If so, can i disable this somewhere?
>
> No.
>
>> connect to bikinibottom.com[208.73.211.70]:25: Connection refused
>> to=<[hidden email]>, relay=none, delay=407,
>> delays=407/0.01/0.15/0, dsn=4.4.1, status=deferred (connect to
>> bikinibottom.com[208.73.211.70]:25: Connection refused)
>
> transport_maps:
>
> bikinibottom.com error:This domain does not accept mail
>

Thank you Ralf

--
Mit Freundlichen Grüßen / Regards

Mario Theodoridis

regify GmbH
Römerstrasse 39 | D-78183 Hüfingen
Amtsgericht Freiburg HRB 709343
Telefon: +49 771 8978 4238
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Re: postfix uses A record for MX less domains

Philip Paeps
In reply to this post by Ralf Hildebrandt-2
On 2017-03-31 15:01:17 (+0200), Ralf Hildebrandt <[hidden email]> wrote:

> * Mario Theodoridis <[hidden email]>:
> > i'm having a curious issue with our postfix instance.
> >
> > It seems it is sending emails to a domain's A record when no MX is found.
> >
> > Is that standard?
>
> Yes.
>
> > If so, can i disable this somewhere?
>
> No.

If you own a domain that should not be receiving email, you can prevent
MTAs trying to send mail to it by explicitly specifying a null MX in the
DNS:

    bikinibottom.com. IN MX 0 .

Philip

--
Philip Paeps
Senior Reality Engineer
Ministry of Information
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Re: postfix uses A record for MX less domains

Mario Theodoridis
On 03/04/17 16:56, Philip Paeps wrote:
> If you own a domain that should not be receiving email, you can prevent
> MTAs trying to send mail to it by explicitly specifying a null MX in the
> DNS:
>
>     bikinibottom.com. IN MX 0 .

Good to know, thanks Philip.

--
Mit Freundlichen Grüßen / Regards

Mario Theodoridis

regify GmbH
Römerstrasse 39 | D-78183 Hüfingen
Amtsgericht Freiburg HRB 709343
Telefon: +49 771 8978 4238
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Re: postfix uses A record for MX less domains

Viktor Dukhovni

> On Apr 3, 2017, at 11:07 AM, Mario Theodoridis <[hidden email]> wrote:
>
>> If you own a domain that should not be receiving email, you can prevent
>> MTAs trying to send mail to it by explicitly specifying a null MX in the
>> DNS:
>>
>>    bikinibottom.com. IN MX 0 .
>
> Good to know, thanks Philip.

Note, this will typically also prevent "the domain" from sending email.
That is, in this example, email from "[hidden email]" will be
refused by many if not most receiving domains.

--
        Viktor.

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