False rejection of valid sender domain

[#1]

@Kwak

Thanks for the mxtools link. Im going to work through some of its suggestions. 

The reason i belive it is plusnet is that the system was working for about a decade without problem or change to my MX record. The only variable has been changes with the Plusnet service.

[#2]

Thanks for confirming @TYN.  I'm no expert on this (though do have some knowledge on it which could be a dangerous thing!), but wouldn't that domain need mx records in order to receive mail? Therefore emails to the stated email address wouldn't be routable?

[#3]

@jelv

Thanks for the suggestion. I prefer to host the mail myself. I once had a very bad experience with hosted mail when an isp went broke and lost all my files (website and emails)

I have been happier taking charge of my own data (until last year).

[#4]

You could still host the mail yourself: move the domain registration and name servers away from Plusnet and it would all be under your own control.

Plusnet are not going to give any issue priority unless it is affecting hundreds or thousands of users.

[#5]

The problem with that is outgoing mail and reputation-based spam filtering. A dynamic IP will suffer badly, and even a static address may struggle if you don't send enough mail to earn a positive reputation. The reliance on the ISP's mail server therefore continues (the alternative being a paid 3rd party).

[#6]

This topic was started over a year ago and TYN first posted last April. It appears very few users are affected so I'd guess with all the other issues Plusnet have at the moment it could be some time before it is fixed and there's no guarantee if they do sort it it won't go wrong again.

People have to assess how much it is worth to have reliable email - I'd of thought that for around £25 a year, for many it would be a small amount to pay for a reliable service.

[#7]

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@TYN wrote:
I once had a very bad experience with hosted mail when an isp went broke and lost all my files (website and emails)

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Keeping your own backup is the obvious solution to that!

[#8]

@pjmarsh

Hey, Im thankful for you simply trying to be helpful. I did have an MX record, the system/configuration was working for years. Good news is that I've found a solution of sorts so will post details below.

[#9]

@jelv

Thanks for your suggestion, the thing is, the domain name/nameservers for my main website were never with Plusnet in the first place. I just hosted it via a Plusnet static address and used thier hosting space as an emerency backup.

The issue for me was never one of refusing to pay £25 pa, more not wanting to lose an IP address I've used for over a decade and the absolute flexibility I have hosting my own site/email. Other than this particular issue and a few minor hiccups over the years, Plusnet has provided me with superb service, thats why I've stayed loyal.

I've just finished reading your post about why you left and I agree with most of it. Especially the loss of the ticket system and issues with breadth of tech knowhow when contacting customer services. From the sounds of it I think I've been with the company as long as you (I moved to them after compuserve and lycos!). Back in those days few people knew who Plusnet were, but for those that did, their reputation was second to none.

Ps. I did have a backup, but back then I did them every few months. I suspect a decade later, even with terabyte hard drives, there are still not many people who download their data from their isp servers on a daily/weekly basis.

[#10]

@RandallFlagg

I was wrong about the source of my new problems and owe the Plusnet team an apology. Sorry. Last week I added some custom rules to my spam filter and after looking through my mail servers security logs I could see one of them was aggressively rejecting messages. Disabling the rule has restored some of my traffic.

@ All
 
I think I've found a solution of sorts and want to share the process although this may only apply if youre hosting your own mail server like me.

Using https://mxtoolbox.com/SuperTool.aspx was key to helping solve many of the issues I was facing. A check on my mail server's fqdn revealed three main issues:
    
    1. My DMARC/DKIM/SPF settings were not configured well
    2. My mailserver DNS record was not being found
    3. My I/P address was blacklisted by Spamhaus ZEN
   

Solutions (in order of problems):
    

1. Setup DMARC Email Security (including SPF and DKIM) using guide on link below
    https://www.esecurityplanet.com/applications/how-to-set-up-implement-dmarc-email-security.html
    
If your mailserver is using Plusnet to relay messages then when creating a SPF record in DNS settings for domain (TX record) it should include plusnet relay details e.g. -  "v=spf1 mx:[Plusnet account name].plus.com -all"
    
Note: The only problem with this is that the public dkim key for the alias wont match your private key. This would probably be resolved if Plusnet setup an reverse ptr record matching your servers fqdn (see below) but so far I've not yet noticed any problems.
    
2. To resolve any SMTP Banner Mismatch, ensure the 'internethostname' setting on the mail server is - [Plusnet account name].plus.com
    
    OR    

Request Plusnet to setup a reverse (PTR) record that matches the hostname of your mail server (I dont think they will do this but it is a crucial long term solution to solving these issues. I wish they would just add this as a control panel feature for those with static IPs, along with a facility for us to change our usernames to match external domain names we own)
    
3. Plusnet adressess are automatically added to the Spamhaus ZEN list. You can go to the Spamhaus website and request removal of your IP if you have a static address and are using a mail server.

And thats pretty much it. Im checking my logs everyday to see which emails are being blocked, I've had family and friends send me messages to test that I can recieve emails again, and just as important - when I send a reply its not being returned as undelivered.   
    
I hope this is useful and helps others in similar situations as I was. After a year of waiting, I finally feel that I am that bit closer to solving my plusnet/email problems. 🙂

[#11]

 If your mailserver is using Plusnet to relay messages then when creating a SPF record in DNS settings for domain (TX record) it should include plusnet relay details e.g. -  "v=spf1 mx:[Plusnet account name].plus.com -all"   

 That record is wrong as it assumes symmetrical inbound/outbound mail which isn't necessarilly the case. If you are relaying via Plusnet it should be:

"v=spf1 mx include:madasafish.com -all"

Note: The only problem with this is that the public dkim key for the alias wont match your private key. This would probably be resolved if Plusnet setup an reverse ptr record matching your servers fqdn (see below) but so far I've not yet noticed any problems.

It sounds like you might be getting confused here as DKIM has nothing to do with SPF. Given that you control the DNS for your domain you can publish the public key that is linked with the private key your server uses. 

    
2. To resolve any SMTP Banner Mismatch, ensure the 'internethostname' setting on the mail server is - [Plusnet account name].plus.com
    
    OR    

Request Plusnet to setup a reverse (PTR) record that matches the hostname of your mail server (I dont think they will do this but it is a crucial long term solution to solving these issues. I wish they would just add this as a control panel feature for those with static IPs, along with a facility for us to change our usernames to match external domain names we own)

 The names don't need to match - all that is usually required is that the reverse PTR lookup resolves to a name that subsequently resolves to the same IP address.

 We have drifted way off-topic here though so please start a new thread if you wish to discuss further as it may distract from the core issue that this thread is about.

[#12]

@MJN

Opps. Sorry for the error. Im not an expert and most certainly don't want to give out wrong information. My relay server hostname (but not internet host name) is "relay.plus.net" and i've just changed my spf record to match it to see what happens.  

Incidentally the moment I posted that last message I tried another website test, this time at: http://www.appmaildev.com/en/dkim

Sadly, I received my first after my mods "<test-xxxxx@appmaildev.com> (relay.plus.net: 550 <xxxxx@ligali.org> sender rejected - invalid domain (no MX or A record))" - So although I can now receive and send some emails, it looks like ive jumped the gun a bit so I'm still posting here because the initial problem remains.

But you have me puzzled.

You wrote "The names don't need to match - all that is usually required is that the reverse PTR lookup resolves to a name that subsequently resolves to the same IP address."

This is confusing. Obviously my own plusnet assigned static IP address is not the same as the resolved relay.plus.net IP address. How can these two unmatched domain names share the same IP address for the reverse PTR lookup as you suggest? Even madsafish.com doesn't resolve to relay.plus.net

I understand you may not want to explain in any detail (I may not even understand!) but seeing that the error which occurs seems linked to this missmatch it all seems relevant. Anyway, I hope my mistakes and successes will be useful to others in solving the issue while the Plusnet team are struggling to address it. Im happy to be able to send and receive some emails when seven days ago I was getting nothing both ways!

[#13]

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@TYN wrote:

@MJN

Opps. Sorry for the error. Im not an expert and most certainly don't want to give out wrong information. My relay server hostname (but not internet host name) is "relay.plus.net" and i've just changed my spf record to match it to see what happens.  

Incidentally the moment I posted that last message I tried another website test, this time at: http://www.appmaildev.com/en/dkim

Sadly, I received my first after my mods "<test-xxxxx@appmaildev.com> (relay.plus.net: 550 <xxxxx@ligali.org> sender rejected - invalid domain (no MX or A record))" - So although I can now receive and send some emails, it looks like ive jumped the gun a bit so I'm still posting here because the initial problem remains.

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That's an issue with Plusnet's mail server (and the subject of the thread) - there's nothing you can do to prevent it (as far as we know).

You wrote "The names don't need to match - all that is usually required is that the reverse PTR lookup resolves to a name that subsequently resolves to the same IP address."

This is confusing. Obviously my own plusnet assigned static IP address is not the same as the resolved relay.plus.net IP address. How can these two unmatched domain names share the same IP address for the reverse PTR lookup as you suggest? 

We should probably take a step back. What's the reason for you wanting the forward and reverse lookups to match? One type of anti-spam measure does perform such a check but you will already pass that - Plusnet static addresses have PTR records with forward records to match. If your desire is in the context of SPF checks there are no reverse lookups performed. The SPF record is parsed for IP addresses explicitly listed and implicitly referenced by name. The sending IP address (which would be Plusnet's outbound mail server) is checked against this list.

Even madsafish.com doesn't resolve to relay.plus.net

Relay.plus.net is the name of the smarthost you send your mail to/through. It is not the machine that then sends it out on to the Internet.

[#14]

I have a thread on AVASOUTn rejecting outgoing emails due to "virus", but thought I would piggyback on here due to sporadic but regular issues with rejections due to "invalid domain". 

I notice it's mentioned above that not many are getting this, but add me to the list. There's not really a pattern, and the error does suggest the problem is in the plusnet server, as it's falsely reporting that domains such as mail.com & gmail.com have no A record.  

I get messages like this:

Delivery has failed to these recipients or groups:
Rob Gmail (xxxxxxxxrob@gmail.com)
Your message couldn't be delivered and there was no valid enhanced status code being issued by the remote mail system to determine the exact cause, status: '550 sender rejected - invalid domain (no MX or A record)'.
Rob (xxxxxxx@mail.com)
Your message couldn't be delivered and there was no valid enhanced status code being issued by the remote mail system to determine the exact cause, status: '550 sender rejected - invalid domain (no MX or A record)'.
The following organization rejected your message: avasout07.





Diagnostic information for administrators:
Generating server: EXCHANGE1.ad.domain.co.uk
robxxxxxx@gmail.com
avasout07
Remote Server returned '550 <rob@domain.co.uk> sender rejected - invalid domain (no MX or A record)'
xxxxxx@mail.com
avasout07
Remote Server returned '550 <rob@domain.co.uk> sender rejected - invalid domain (no MX or A record)'

This morning for example, I sent an email 3 times which was rejected as above twice. On the third time it went through.
I have read the tips regarding SPF and DMARC and the spamhaus blacklist above - indeed we are on a fixed IP and were on the ZEN blacklist so have delisted that so thanks @TYN  for that tip. But this problem evidently isn't spamhaus but something in the mail relay. 

We send via Exchange 2016 to relay.plus.net

So this happens randomly, without ability to replicate, but does happen to us regularly.

I can send email/headers privately if anyone thinks they would be of use. 

thanks - Rob

[#15]

@robatworkuk

Hey, i'm just glad my comments were of some use. 

For the first time in ages I seem to be experiencing something close to a normal service but its definitely the unpredictability that makes the problem so infuriating and hard to track down. I hope Plusnet find a solution to our shared problem.