Hotmail rejecting mail from PN [Diagnostic-Code: smtp; 550 5.7.1]

[#1]

Hi,

I'm new to this forum but having exactly the same problem: namely an email I send from a plusnet address to a hotmail address is being consistently rejected with the 550 5.7.1 error message.  I get the same problem even with a single addressee and no attachment.

What's the best way forward please?

Many thanks!

[#2]

Just as an aside, given the amount of spam I have been receiving from PlusNet e-mail addresses over the last few days I'm not really surprised that we have got on Hotmail's blacklist  

[#3]

Here's a thought...  are they actually coming from PN or are they coming from Greenby? All these problems seem to have started in the last twelve months or so. Coincidence!?

Anyone care to offer proof either way?

[#4]

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@Digsy wrote:

Just as an aside, given the amount of spam I have been receiving from PlusNet e-mail addresses over the last few days I'm not really surprised that we have got on Hotmail's blacklist  

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Except, they are not coming from PN's servers, rather Amazon's AWS.

[#5]

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@Lordwotsit wrote:

Here's a thought...  are they actually coming from PN or are they coming from Greenby? All these problems seem to have started in the last twelve months or so. Coincidence!?

Anyone care to offer proof either way?

---

See above.

[#6]

From the message source, the last spam message has a Plusnet Public IP [51.9.140.133]
and departed via avasout-ptp-003.plus.net [84.93.230.244]

The SPF / DKIM / DMARC are all PASS.

[#7]

@PhilipHeyes 

Thanks for the info... although I confess most of the NW acronyms & IP messages "do my head in" to coin a phrase. Having been brought up on IBM 360 SysProgging

Does that give any clues as to where the problem lies?

More to the point, will this ever be fixed?

[#8]

Damn the Bezos bloke....

[#9]

I use a Globalnet email and am getting the same issues today (31/1/26) - with the same IP address being flagged 

Reporting-MTA: dns; avasout-peh-002 [84.93.238.88]
Received-From-MTA: dns; [192.168.68.107] [86.20.124.117]
Arrival-Date: Sat, 31 Jan 2026 22:17:52 +0000

Final-recipient: rfc822; xxxxxxx@hotmail.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [212.159.14.18] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BCC208B81DFD34] [SG2PEPF000B66CD.apcprd03.prod.outlook.com 2026-01-31T22:17:54.030Z 08DE61045C425675]

Last-attempt-Date: Sat, 31 Jan 2026 22:17:54 +0000

[#10]

As an aside, I really don't understand how this can happen. Being part of BT, PlusNet et al are the UK#s biggest ISP by some considerable margin (at least according to these stats). Surely another network deciding that the whole thing on block isn't something that the intern could to on a Friday afternoon when he's late meeting he colleagues in the pub? I would imagine that should be some kind of "nuclear option" which would only be invoked after several warning messages to the tune of "we are getting a ton of spam from your servers, you have until <insert deadline here> to sort it OR THEN we will block all PN servers".

It just seems nuts to me. It's like LG suddenly deciding that nobody can watch the BBC on their TVs anymore because they got the weather forecast wrong. Unless of course this has already gone on in the background and the PN management weren't able to get on top of the problem in time.

Anyone know how these policies actually work behind the scenes?

[#11]

212.159.14.20 also getting the same error - twice today at 14:37 and 17:01

Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [212.159.14.20] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BCC175049B6541] [BL6PEPF00022570.namprd02.prod.outlook.com 2026-02-01T14:37:16.391Z 08DE60BA83212770]

[#12]

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@Digsy wrote:

Anyone know how these policies actually work behind the scenes?

---

No idea but it's a safe bet that there will be no humans involved in triggering the block.  'Systems' on the receiving server(s) will keep a track of incoming messages and when the level of spam from an IP address reaches a certain level, that IP address is put on a naughty list and thus nothing more from that IP address is accepted.

[#13]

@stuck @Digsy 

"Please remove the unkown item from the bagging area!"

"Please remove the unkown item from the bagging area!"

"Please remove the unkown item from the bagging area!"........

[#14]

Microsoft LIVE rejecting this morning  :

Reporting-MTA: dns; avasout-peh-004 [212.159.14.20]
Received-From-MTA: dns; relaptop [86.30.96.254]
Arrival-Date: Mon, 02 Feb 2026 09:58:32 +0000


Final-recipient: rfc822; jxxxxxxxxon@live.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [212.159.14.20] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BCC1272ACF301E] [DU2PEPF00028CFE.eurprd03.prod.outlook.com 2026-02-02T09:58:32.848Z 08DE609397A12345]

Last-attempt-Date: Mon, 02 Feb 2026 09:58:32 +0000

[#15]

As a complete aside - forum notification emails from this forum are now getting bad spam scores, primarily down to the hidden tracking pixel url buried in each message