[Outages-discussion] [outages] CableOne DNS issue?

[Greg Dickinson]

Are we certain that MX records aren't required?  Per the RFC:

" The lookup first attempts to locate an MX record associated with the
   name.  If a CNAME record is found, the resulting name is processed as
   if it were the initial name.  If a non-existent domain error is
   returned, this situation MUST be reported as an error."

Greg Dickinson
Network Engineer | Bryant Bank

O: 205-917-2407  C: 205-234-6427
www.bryantbank.com



-----Original Message-----
From: Outages-discussion [mailto:outages-discussion-bounces at outages.org] On Behalf Of Jeremy Chadwick
Sent: Friday, March 24, 2017 11:50 PM
To: frnkblk at iname.com
Cc: outages-discussion at outages.org
Subject: Re: [Outages-discussion] [outages] CableOne DNS issue?

With regards to the first paragraph only: SMTP MTAs, per RFC 5321 Sec 5, should attempting connect to the DNS A record of the recipient domain.
In other words: an MX record isn't necessarily required for SMTP flow (it's always highly recommended, however).

Of course, if the MX record would normally point to an FQDN which has a different A record than the domain itself, then that would certainly cause problems.  Same goes for if the authoritative NSes aren't resolving the domain's A record at all (your second paragraph).

-- 
| Jeremy Chadwick                                   jdc at koitsu.org |
| UNIX Systems Administrator                http://jdc.koitsu.org/ |
| Making life hard for others since 1977.             PGP 4BD6C0CB |

On Fri, Mar 24, 2017 at 09:27:01PM -0500, frnkblk--- via Outages wrote:
> Was just alerted that our outbound email queues have a few messages to 
> cableone.net queued up, because there's no MX record (even Google and 
> OpenDNS don't have an MX record cached).
> 
>  
> 
> DNSInspect (http://www.dnsinspect.com/cableone.net/10059114) is 
> showing that their two nameservers aren't resolving their A record.
> 
>  
> 
> DownDetector is reporting issues: 
> http://downdetector.com/status/cable-one
> 
>  
> 
> There's also few posts on Twitter, too: 
> 
> https://twitter.com/lucky_boym/status/845441576973295616
> 
> https://twitter.com/AnonySerb/status/845441954599092224
> 
>  
> 
> And just now posted, from CableONE:
> 
> https://twitter.com/cableONE/status/845460682560688128
> 
>  
> 
> Frank
> 

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