Odd problem with incoming messages rejected

[#1]

In the past few days some incoming emails to one of our PlusNet email addresses have been rejected and returned to sender. I've been able to see one of the returned messages and it says 

   (reason: 552 Spam Message Rejected )

However:

 - so far we're aware of 4 different senders this has happened to, 2 use gmail, 1 uses hotmail and the other is hshants.org.uk

 - all have sent emails in the past with no problems, and some emails from them still get through

 - some of the emails were replies to us, others originated with the sender

 - sometimes the rejected email was resent and it got through on the 3rd or 4th attempt

Is that normal spam filter behaviour?

Any suggestions on how to fix this?

Chris.

[#2]

Hi there Chris, I'm really sorry to see this. could you send me a DM with your username please and if possible a copy of the headers from one of the returned messages? - Adam

[#3]

Thanks for sending this across Chris, are you able to have them send you just a blank email with nothing attached at all and see if you get this? It sounds like the spam filter is blocking their emails.

[#4]

@csmith94 

I think that is known - the question is why are the spam filters profiling these emails in the manner it is?

A blank email will at best prove that the source address alone is not the cause.

Did the NDR headers returned by the OP contain the SPAM signature?  If yes, has that signature been inspected by the email support team?

[#5]

Thanks for all the replies. Just to emphasize some points:

•  some of the senders of the rejected emails have since sent other emails that have got through successfully.
•  one of them repeatedly sent the rejected email and that got through on the 3rd or 4th attempt
•  we asked one of the others to forward the rejection email she received (the one I gave Adam Walker the details of), she sent that to the same address as the rejected email and it got through 
•  most of the emails were simple, no links or attachments, a couple were short replies to emails we'd sent

That we've since received other emails from the senders suggests it's not the senders that are being blocked. That some of the emails were short and simple, and in particular that one of them got through with repeated attempts to send it, suggests to me that it's not the content being blocked. I'm puzzled!

[#6]

@ChrisK99 

Looking through the original header and what you've now confirmed, what ever was attached is stopping the email from being sent across. If you're using webmail, any attachment over 7mb won't send and on email clients, this is bumped up to 100mb. 

In this scenario, there isn't much more we can do unless there were emails being blocked that had no attachments. If the original email didn't have any attachments either, please let me know but by the looks of it, it did. 

[#7]

Thanks for the reply, but there wasn't an attachment. We sent a simple email, no links or attachments, and the other person replied with a short message, a couple of lines, no links or attachments. That reply was rejected.

Chris.

[#8]

I'm having the same problem with all emails from one gmail address, with and without attachments.  Messages got through OK up to December 2022 but this month they have all been rejected with the same reason, 552 Spam Message Rejected.  I've asked the sender to send to my gmail address instead.  I can forward the messages manually from my gmail to my plusnet, but automatic forwarding from gmail fails with the same reason given.

[#9]

To be clear - if the sender sends a blank email containing nothing but your PLUSNET email address, a subject and minimal plain text (no signature block) it will be rejected?

Is your sender running their own email server?

[#10]

There has never been a signature block but the blocked messages did contain several lines of text.  Two test messages with only a few words of text have arrived OK.

Since my first post, one message (plus the 2 tests described above) sent to my gmail arrived successfully using auto forwarding, but others have been rejected and needed to be forwarded manually, which has always worked.

[#11]

Fails when sent to your Plusnet address - to be clear, is that direct to your account.plus.com email address - rather than to some other (own domain address) which redirects to the Plusnet address?

[#12]

Yes, the messages are direct from a standard gmail address to my standard plusnet address, or forwarded from my standard gmail either automatically or manually.

There hasn't been a 'normal' message recently so I don't know if the problem has been solved by plusnet, the tests with short messages both worked.  The last rejection from both gmails was on 13/2/23, auto forward from my gmail worked on 16/2/23.

[#13]

Auto forward and manual forward are significantly different paradigms.

Auto forward needs the forwarding service to have implemented SRS so as to not fall foul of SPF verification.

I am not saying the such is perinate to your experience, but you do need to know that they are not comparable tests.