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False rejection of valid sender domain

MJN
Pro
Posts: 1,162
Thanks: 74
Fixes: 3
Registered: ‎26-08-2010

False rejection of valid sender domain

Hi Plusnet,

 

Following on from my previous report about this issue I have today received a delivery failure for an email sent out through relay.plus.net:

 

The mail system

<<removed>@tapsuk.net>: host relay.plus.net[212.159.9.107] said: 550
    <<removed>@newtonnet.co.uk> sender rejected - invalid domain (no MX or A
    record) (in reply to MAIL FROM command)
Reporting-MTA: dns; secure.newtonnet.co.uk
X-Postfix-Queue-ID: 0F704241DDB
X-Postfix-Sender: rfc822; <removed>@newtonnet.co.uk
Arrival-Date: Tue, 29 Oct 2019 10:09:50 +0000 (GMT)

Final-Recipient: rfc822; <removed>@tapsuk.net
Original-Recipient: rfc822;<removed>@tapsuk.net
Action: failed
Status: 5.0.0
Remote-MTA: dns; relay.plus.net
Diagnostic-Code: smtp; 550 <<removed>@newtonnet.co.uk> sender rejected - invalid
    domain (no MX or A record)

 

 

Is there anything that can be done about this please? It has been many months since I last saw the issue and so to see it return is rather disappointing, particularly given it was first reported so long ago (Nov '17).

 

9 REPLIES 9
Plusnet Help Team
Plusnet Help Team
Posts: 15,084
Thanks: 4,649
Fixes: 778
Registered: ‎21-04-2017

Re: False rejection of valid sender domain

Hi @MJN I'm sorry to see you're experiencing this problem. Could you send me a PM with the full email addresses you're sending from and to and I'll be happy to get this raised over to our NetOps team to investigate further. 

If this post resolved your issue please click the 'This fixed my problem' button
 Anoush Mortazavi
 Plusnet Help Team
MJN
Pro
Posts: 1,162
Thanks: 74
Fixes: 3
Registered: ‎26-08-2010

Re: False rejection of valid sender domain

PM sent. Thanks Anoush! 🙂

Plusnet Help Team
Plusnet Help Team
Posts: 1,030
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Registered: ‎22-01-2018

Re: False rejection of valid sender domain

Thanks for getting back to us@MJN,  I have raised this to our NETOPS team and we will keep you updated here.

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 SammyM
 Plusnet Help Team
MJN
Pro
Posts: 1,162
Thanks: 74
Fixes: 3
Registered: ‎26-08-2010

Re: False rejection of valid sender domain

Thanks Sammy!
Plusnet Help Team
Plusnet Help Team
Posts: 15,084
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Registered: ‎21-04-2017

Re: False rejection of valid sender domain

No problem, we'll update you as soon as we know more.

If this post resolved your issue please click the 'This fixed my problem' button
 Anoush Mortazavi
 Plusnet Help Team
Plusnet Help Team
Plusnet Help Team
Posts: 15,084
Thanks: 4,649
Fixes: 778
Registered: ‎21-04-2017

Re: False rejection of valid sender domain

Hi @MJN We've done some digging into this and it looks like this repeatedly failed to resolve and was rejected by us after the sixth failed lookup over a period of 30 seconds. This could have been caused by any number of things that interrupt DNS requests. We've done work on our side which should reduce the likelihood of the issue being caused by us.

It's difficult to advise what the issue was caused by though as it could've come from anywhere along the chain, one possibility is that the A and MX records of the domain all have a short TTL and the name servers are on the domain itself, so this may have caused records to expire or issues reaching the name servers.

I'd recommend keeping an eye on this and let us know if you notice this problem crop up frequently.

I hope this helps.

If this post resolved your issue please click the 'This fixed my problem' button
 Anoush Mortazavi
 Plusnet Help Team
MJN
Pro
Posts: 1,162
Thanks: 74
Fixes: 3
Registered: ‎26-08-2010

Re: False rejection of valid sender domain


@Gandalf wrote:

Hi @MJN We've done some digging into this and it looks like this repeatedly failed to resolve and was rejected by us after the sixth failed lookup over a period of 30 seconds. This could have been caused by any number of things that interrupt DNS requests. We've done work on our side which should reduce the likelihood of the issue being caused by us.

 


Thank you so much for looking into this further; I appreciate it's not the most appealing type of problem to investigate given it doesn't manifest itself permanently. I also recognise that email isn't really the primary service you are selling here, although its functionality is important to me.

It did seem to me that it was a DNS resolution failure that as leading to this and so it is good that you were able to positively confirm this.

One thing that occurred to me is that I can understand you performing a DNS lookup to confirm the existence (or not) of the sender domain however this check should only be acting on an NXDOMAIN result as that is the only outcome that proves a domain doesn't exist. The lack of a DNS response doesn't prove anything either way and shouldn't, IMHO, be used as the basis for rejection. Perhaps that is the change you speak of?

 

It's difficult to advise what the issue was caused by though as it could've come from anywhere along the chain, one possibility is that the A and MX records of the domain all have a short TTL and the name servers are on the domain itself, so this may have caused records to expire or issues reaching the name servers.


Agreed. Whilst I am confident in the availability of my DNS provider I am not in a position to say whether or not they did have an issue when this email was being sent. That said, the multiple nameservers should be providing redundancy and resilience such that even if a problem were affecting one of their servers the other should be still available.

 

I'd recommend keeping an eye on this and let us know if you notice this problem crop up frequently.

I hope this helps.


It does; thank you again. 

Plusnet Help Team
Plusnet Help Team
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Registered: ‎21-04-2017

Re: False rejection of valid sender domain

Thanks for getting back to me @MJN 

No problem, I'm seeing if I can find out the answers and clarification and will let you know when I know more.

If this post resolved your issue please click the 'This fixed my problem' button
 Anoush Mortazavi
 Plusnet Help Team
Plusnet Help Team
Plusnet Help Team
Posts: 15,084
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Registered: ‎21-04-2017

Re: False rejection of valid sender domain

Hi @MJN Sorry for the delay. Admittedly I got a response from a colleague about this on the 4th Nov which slipped my mind until now. Sad

So while it may not be ideal, there’d have to be something in place to minimise the potential for abuse of the system. The repeated lookups were put in place to fix the original issue, where there were repeated and widespread failures.

I hope this helps again. Smiley

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 Anoush Mortazavi
 Plusnet Help Team