VS: Dumb Question is an A or AAAA record required?

Thu Jul 9 14:38:38 UTC 2020

Many spammers send in addition to MX to A records, if available.  Still, it is a good practice to not to publish an A record for the mail zone, if not specifically needed for something else.  Of course if it points to somewhere else than the receiving SMTP server, not much harm done mail-traffic-wise.

Jukka

-----Alkuperäinen viesti-----
Lähettäjä: bind-users <bind-users-bounces at lists.isc.org> Puolesta Matthew Richardson
Lähetetty: 9. heinäkuuta 2020 16:06
Vastaanottaja: bind-users <bind-users at lists.isc.org>
Aihe: Re: Dumb Question is an A or AAAA record required?

On a related issues there were (perhaps long ago) issues if the A record for a domain had an SMTP server on it, where email could sometimes be delivered to that A record rather than the MX.  I had (again long ago:
10-15 years) actually seen this occur.

Do people think that this problem could still occur these days?  What sort of transient (presumably DNS) failure might cause an SMTP server to deliver to A rather than MX?

Best wishes,
Matthew

 ------
>From: Anand Buddhdev <anandb at ripe.net>
>To: "@lbutlr" <kremels at kreme.com>, bind-users 
><bind-users at lists.isc.org>
>Cc: 
>Date: Thu, 9 Jul 2020 14:43:04 +0200
>Subject: Re: Dumb Question is an A or AAAA record required?

>On 09/07/2020 14:21, @lbutlr wrote:
>
>> Given a domain that is hosted and used for email and web, is an A 
>> record for that domain actually required?
>
>It's not *required*. But see below.
>
>> That is, if bob.tld is hosted by example.com can you simply have
>> 
>> 	NS ns1.example.com
>> 	NS ns2.example.com
>> 	MX mx.example.com
>> 
>> www	CNAME www.example.com
>> 
>> Without specifying
>> 
>> 	A 11.22.33.444
>
>These days, many folk try to reach websites by typing just the bare 
>domain name without the "www" prefix.
>
>If a user types "bob.tld" into a browser, the browser will issue an 
>address lookup for "bob.tld", causing the resolver to ask for A and 
>AAAA records for "bob.tld". If you don't have an A record at the zone 
>apex, the browser will not get back any address and display an error 
>message for the user. An alert user might try "www.bob.tld" but most 
>users are likely to just give up.
>
>So while it's not *required* to have an address record at the apex, 
>it's good practice to have one.
>
>Anand
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