Plusnet Email servers giving random SMTP 550 errors for inbound emails

[#1]

Agreed … if the software supplier will accept that the issue is a "defect" and deployment of that modified version of software is viable having taken into consideration other changes which might ship with that fix.

If it were to be the case that here we are looking at a DNS look up query failure (rather than a success reporting domain not known) then it is disappointing that the calling code does do discern the difference here and take a more appropriate course of action, rather than treating a generic failure event to imply the domain does not exist.

[#2]

If this is an issue with third-party equipment then I am surprised that my client has never ever seen it with anything other than the PlusNet hosted email addresses out of the >10k different members that they regularly email.

[#3]

The weeks roll on and Plusnet continue to ignore this.

Another Plusnet customer doesn't receive another email from a valid domain:

From: "Mail Delivery System" <Mailer-Daemon@xxx>
To: xxx
Sent: 15/01/2019 08:08:41
Subject: Mail delivery failed: returning message to sender

This message was created automatically by mail delivery software.
 
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
 
xxx.xxx@xxx.plus.com
host mx.avasin.plus.net [212.159.8.200]
SMTP error from remote mail server after MAIL FROM:<xxx.co.uk> SIZE=14495:
550 #5.1.8 Domain of sender address <xxx.co.uk> does not exist

I resent this email. But I wonder how many people don't bother, resulting in Plusnet customers missing email. Thousands per day perhaps?

[#4]

Hi, I just started a new thread on this and staff member BD thankfully pointed me to this thread, I hadn't realised this was an ongoing problem.

I've not read every post, for me I didn't realise the emails were bouncing until today from other people until someone told me, but I have had problems SENDING emails from my domain the last while, and if I retry it normally works. Are others aware of/seen this? So it sounds like same problem and a similar "component", I'd suggest? My email client randomly says an error basically of "this sender domain does not exist" = exactly same.

Until they fix it I'd suggest a quick botch "fix" is to not immediately reject emails out hand for this error, but instead retry failed emails X times (perhaps with a delay), preferably trying different DNS servers (if they have this distribured ) to see if it is one of them that is broken? Log any of those that failed and then those that worked to see if there is a pattern?

Workaround it AND diagnose it.

It's not a nice problem as it not only means I might miss emails it sends my plusnet details back to the original sender.

[#5]

Thanks for the update and suggestions, @Kwak.

I'll check in with our projects team tomorrow and see if there's any further update on this.

Best wishes

Dave

[#6]

I can also confirm that this is still happening and provide examples if you still need more. These failures are blocking automated messages to Plusnet mail accounts (order acknowledgements, etc.) which can't be set to automatically re-send as the NDRs go back through a separate route to be manually checked.

[#7]

If it WAS to be treated as spam for some reason, why isn't it going into a spam folder?

(Talking of bad spam filters I had to laugh the other day when I logged onto a rarely used outlook account to see Microsoft putting its own emails into the junk folder ;))

[#8]

It isn't an issue of mail being treated as spam, it is a very specific rejection of the mail due to a failure of the Plusnet systems to successfully validate a perfectly valid and correct domain name.

[#9]

Hello Guys,

We are still investigating the issue and currently don't have an update at the moment. I am really sorry and appreciate all the suggestions you have put forward.

Please bear with us.

[#10]

Are you *actively* investigating it - i.e. you have an engineer assigned to the problem who is actually looking at things, or are you just pretending to?

I suspect the later!

[#11]

If they have multiple internal DNS servers to carry the load then .. well my instinct is you'd think there are two ways a random thing like this could happen? One is a code fault (how hard is it to look up a string and say "exists/doens't?" ,and I'd guess it's running some standard software to do it anyway), the second is one of the machines has an incomplete/corrupt database of DNS records. Is it possibly that simple? Load spread over like 10 servers and if randomly the request is given to server # 4 it fails for some records, can that be easily tested internally on a known failing domain? I've no idea how they are set up there end end but as an outsider that a scenario I'm wondering about.

[#12]

If it were that easy it would have been fixed a long time ago.  This has all the hallmarks of a timing issue somewhere in the network.

There are indeed a multitude of DNS server instances … all behind intelligent network switches and load balancers.  It would be presumptuous to assume that this is a straight forward DNS look up "mistake".

[#13]

Can you guys PLEASE elevate fixing this serious error? I just tried to send an email and this time I took a copy of it, email client said: "An error occurred while sending mail. The mail server responded: sender rejected - invalid domain (no MX or A record). Please verify that your email address is correct in your account settings and try again." So it's clearly not fixed? I expected an email in response to something this week (it would probably have been automated) and I now have no idea at all if it was sent to me, not sent, sent and bounced by plusnet as you've a known email problem bouncing valid emails and aren't fixing it? As it was an automated email, it probably wouldn't be resent if plusnet bounced it. I have no idea now what emails I might miss, as I now can't trust plusnet to forward my emails properly :( Of course email is never going to be 100% but when plusnet have a known serious problem with email reported by many people surely you should escalating fixing it as a priority? Is anyone working on it?

[#14]

This problem badly affects systems using automated mail. We manage an ecommerce site for one of our clients and PlusNet users frequently don't receive order acknowledgements or confirmations due to Plusnet bouncing them (they are not re-sent). The users then message the site to complain that they haven't received any confirmation, which creates extra admin, but of course there is a random chance (generally much worse than 50%) that they don't receive the response either. After a couple of rounds of this the Plusnet (non)recipient is usually getting understandably angry and concerned that they have been scammed and threatening all sorts of bad reviews and retribution. The site owner then gets understandably annoyed with us for not fixing the problem and Plusnet just continue to say for 14 months now that they are looking into it. If we could actually successfully send a message to all of the site's users with Plusnet hosted addresses we would advise them to find a more responsive ISP at their earliest opportunity.

[#15]

If it's something timing out, then increase the timeout? And add doing retries on failure? I'm struggling to understand why they can't attempt to fix this, These would be standard workarounds to atttempt for a random error as an attempt to mitigate it? It seems to be a very repeatable (but random) error, repeatable in that it shows the same symptoms and we know it's intermittent so an internal retry would hopefully fix it? I've been mostly concerned here with forwarded emails being bounced that are translated via "my domain" (as that's how the forwarded email works and most of my emails are throgh my domain) but I've realised it might be totally general and affect every email for all users which is a HUGE problem? But if it isn't, can't plusnet say cache all users with known domains routed through plusnet as a first level lookup (or tagged on as a backup lookup upon failure) that'll be a very speedy check if the domain is valid? The list of domains plusnet have to deal with will for their customers with domains will of course be a tiny fraction of all domains. PS I tried whitelisting domain in spam settings, made no difference.

Can they not just switch off the check completely or put it in our junk folder, or allow whitelisting? How much BAD email does it actually help reject anyway? I think users would all rather have a little more spam than have what seems to be a relatively high ratio of valid email totally thrown away

Moderator's note by Mike (Mav): Post released from Spam Filter.