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

[Reindl Harald]

Am 09.07.20 um 16:38 schrieb Jukka Pakkanen:
> 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.

why should it be a good practice not publish an A record?

nothing better can happen than a spammer trying the wrong server at all
as you don't accept random unauthenticated inbound mail on random machines

> -----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?
> 
>> 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.