Dumb Question is an A or AAAA record required?
ondrej at isc.org
Thu Jul 9 14:10:09 UTC 2020
Missing MX, there’s actually syntax accepted by major SMTP servers to disable SMTP for domain:
example.com. MX 0 .
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,
>> From: Anand Buddhdev <anandb at ripe.net>
>> To: "@lbutlr" <kremels at kreme.com>, bind-users <bind-users at lists.isc.org>
>> 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 184.108.40.2064
>> 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.
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