Outgoing plusnet server "relay.plus.net"has blocked me as a spam suspect

[#1]

I copied that topic title because the original is closed.  For the last year I've been sending a (small) group email to half a dozen people with news updates in our professional work.  They are all the same - text and links to (mostly) Government sites and charities. 

Yesterday my mail was stopped by the relay plus server.  I tried without the pdf attachment, I tried to a single recipient, I checked if my 'domain' had been blacklisted, I tried another email client.  I tried to different recipients. All failed. I spent 20 mins with a customer care rep who had no solutions except to "change or tweak your spam or anti virus settings". 

I then had to leave for a meeting, printing off my email to give to people. Embarrassing really as links are not much good on paper. 

I'm clear this is being stopped at the plusnet mail server and although I pointed out and pointed to issues like this before - the CR rep wouldn't accept that.

https://community.plus.net/t5/Email/Plusnet-SMTP-server-incorrectly-rejecting-outgoing-email-as-spam...

The response was: 

"We would not block this in anyway"

So I looked at Spam settings - don't see how they can affect outgoing mail - still tweaked - no change.  I rely on Win 10 defender for antivirus with occasional malware bytes sweep.  No change there. 

If there is some way to check the content of my mail for dodgy stuff - then I will, but it's no different to mails Ive been doing for months. To say the least I am really unhappy about this as I've 'vanished' as far as my clients are concerned and that's not good for the (very little) work I'm hanging onto to pay for my Plusnet fibre for example.

[#2]

I also checked the mail for virus.  None detected.  I see there's a mail from plusnet 1.45pm yesterday from the CR rep saying thanks for my email (?) and that the issue had been passed to technical.  Nothing from them yet.  Meanwhile still cannot send my information update email.

[#3]

OK - since other posts identified http addresses as the issue, I converted the mail to plain text - that was rejected as spam by Plusnets mail server too. 

[#4]

Welcome to the forums @ANTAR  . Probably a silly question, but are all your outgoing emails rejected, or just this specific one?

Could you try sending it via, say, Yahoo, and what the result is?

[#5]

Just this one. I tried via Thunderbird too. The response is instantaneous. No time for reject at other end.

[#6]

I may be wrong, so don't shoot me, but if a message is rejected by the PN server, you should get a notification?

If it is just that one, has anything changed recently?

Using TB would still send via the Plusnet mail server.

[#7]

It’s not by any chance connected with this?   https://community.plus.net/t5/Service-Information/We-re-making-changes-to-your-email/m-p/1598823#M32...

[#8]

I saw that but just using normal PN server

[#9]

@Baldrick1  I don't think so - could be wrong - but the OP says it is only this one email that is causing the error.

Edit - written as @ANTAR  was posting.

[#10]

Message still being identified as spam or virus by server with this message:

552 CoJKhZbXRORPKCoJMh6P6w message rejected due to spam or virus. If you believe this is in error please login to your portal or contact your ISP support team.

I've successfully re-sent an earlier very similar message, but with different content.  So I guess there's something in this individual mail content.  It's not in any way confidential so if anyone has a way to spot problematic content do let me know - happy to post or pm if that's possible. Is there any spam software I can use to identify the trigger - it'll take hours to modify bit by bit to find it that way.

Thanks for all the ideas and help so far.  Very grateful.

[#11]

@bobpullen - are you able to assist here please? Thanks.

[#12]

@ANTAR

Does the email you are sending have an attachment? Does it have links? Does the issue arise to just one addressed or with any addressee?

[#13]

It's likely to be the sender address, one of the recipient addresses, or something in the body of the email (typically a text string or URL) that's causing the false positive.

You're right to assume that altering your spam settings has little influence over your outbound mail, so apologies for the misinformed advice you were given by Support.

If you can private message me with an example of one of the emails that are exhibiting the problem and a list of the sender/recipient addresses then I'll see what I can do.

[#14]

Links aplenty - but all from legit, usually government sources.  Same happens with or without pdf attachment (small).  Also happens in plain-text mode.  I'll send content to Bob.

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[#15]

Just to add that I've just checked that the links work.  All but one did - so I resent without that link - still blocked.