Dumb Question is an A or AAAA record required?

[Ondřej Surý]

Missing MX, there’s actually syntax accepted by major SMTP servers to disable SMTP for domain:

example.com. MX 0 .

Ondrej
--
Ondřej Surý — ISC

> On 9 Jul 2020, at 16:06, Matthew Richardson <matthew-l at itconsult.co.uk> wrote:
> 
> 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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