topic Re: SMTP error 550 5.7.1 part of network is on block list in Email

SMTP error 550 5.7.1 part of network is on block list

ebforum — Wed, 29 Oct 2025 17:14:00 GMT

I have received this bounceback on sending an e-mail from Outlook 365 on my PC using my Plusnet e-mail account to an Outlook.com recipient.

Part of the network on their blocked list?

Reporting-MTA: dns; euk22.eukhosting.net

Action: failed
Final-Recipient: rfc822;xx@yy.org.uk
Status: 5.0.0
Remote-MTA: dns; outlook-com.olc.protection.outlook.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [nnn.nnn.nnn.nn] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BC29117274DD8A] [DS1PEPF0001709C.namprd05.prod.outlook.com 2025-10-29T11:01:47.997Z 08DE1488BC5141F0]

Re: SMTP error 550 5.7.1 part of network is on block list

Leanne_T — Thu, 30 Oct 2025 07:51:36 GMT

Morning @ebforum

Thanks for starting a new thread for the email error message.

I've received the reply to my private message this morning and I will send the details to the relevant team for investigation.

Thanks

Leanne.

Re: SMTP error 550 5.7.1 part of network is on block list

Townman — Thu, 30 Oct 2025 08:20:27 GMT

When they provide a remedy, can you please post back to here what it is, so that future occasions users are informed of the appropriate actions.

Re: SMTP error 550 5.7.1 part of network is on block list

abitpedantic — Thu, 30 Oct 2025 18:40:10 GMT

Presumably this is a different issue from the severe blocklisting that was occurring for many weeks until about 2 weeks ago when it seemed to be resolved and Microsoft-owned addresses could be reached again. Has there been another outbreak of spam?

I note that, unless the sequence of n’s has been mis-typed, the blocked server is not a Plusnet avasout one, assuming their IP addresses haven’t changed (they were 212.159.14.nn and 84.93.230.nnn).

Re: SMTP error 550 5.7.1 part of network is on block list

Silver-Codger — Sat, 06 Dec 2025 02:22:37 GMT

Message to a single Hotmail address repeatedly fails as shown below. Sent using Outlook from a xxxx@yyyyy.plus.com address.

Final-recipient: rfc822; xxxxxxxxxx@hotmail.co.uk
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [212.159.14.17] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BC5D7679360942] [DB1PEPF000509E7.eurprd03.prod.outlook.com 2025-12-05T09:39:59.776Z 08DE2EBB4648F94A]

Last-attempt-Date: Fri, 05 Dec 2025 09:39:59 +0000

I assume these block lists are being investigated?

Re: SMTP error 550 5.7.1 part of network is on block list

stuck — Sat, 06 Dec 2025 18:40:23 GMT

@Silver-Codger wrote:
...I assume these block lists are being investigated?

You would hope so but this block by MS has been going on for sometime now so it seems that MS are not inclined to unblock the offending parts of the PN network.

Now if a Superuser ( @Townman @MisterW) or a member of Plusnet staff @plusnettony @dave) would give us mere mortals an update and correct the impression I give above, I'm happy to be told I'm completely misguided and it will be sorted very soon.

Re: SMTP error 550 5.7.1 part of network is on block list

Townman — Tue, 09 Dec 2025 16:59:44 GMT

Does not help that folks keep creating new threads and post here and there about the same issue!

Re: SMTP error 550 5.7.1 part of network is on block list

stuck — Tue, 09 Dec 2025 17:23:14 GMT

@Townman Agreed, but is it not an indication of the extent of the problem and the annoyance it is causing users? When people are irritated they tend to just speak out rather than slowing down and taking the time to search for existing topics about their problem.

Perhaps if one of the many topics was pinned people would see it and thus be more inclined to post in one place?

Re: SMTP error 550 5.7.1 part of network is on block list

Townman — Tue, 09 Dec 2025 17:50:46 GMT

I cannot disagree with the merits of pinned and clearly titled threads for common issues. It has been discussed!

@James_B

Re: SMTP error 550 5.7.1 part of network is on block list

TrevorP — Fri, 20 Feb 2026 12:22:00 GMT

@Leanne_T

I've read thru the (extensive) prior thread of some 56 pages and found myself redirected here. I also fairly suddenly, find myslef unable to forward a flight confirmation email to my wife on a nnn.nnn@live.com address from my email@nnnn.plus.com account, with the following error message:

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=11BCD858D5F5BAF3] [AM2PEPF0001C716.eurprd05.prod.outlook.com 2026-02-20T12:10:37.420Z 08DE6C2C72DFCDAE]

Interestingly, if I use my outlook.com address [from same Outlook client] the mail makes it thru.

Would be pleased to have an update on this apparently long running issue. Thanks,

Re: SMTP error 550 5.7.1 part of network is on block list

Leanne_T — Sat, 21 Feb 2026 06:58:20 GMT

Hi @TrevorP

Thanks for coming back to the community.

Could you let me know some further information, such as the mail headers and any bounce back messages? If these contains personal details, send this to me in a private message.

Details on finding this can be found in the Obtaining email headers page.

Leanne.

Re: SMTP error 550 5.7.1 part of network is on block list

stuck — Fri, 20 Feb 2026 17:19:36 GMT

@Leanne_T If you can fix this users problem as easily as your reply to him implies, then please also fix the same problem which has been afflicting lots and lots of users for a long time now. This six page 89 replies and counting topic that I created weeks ago would be a very good place for you to start:

https://community.plus.net/t5/Email/Hotmail-rejecting-mail-from-PN-Diagnostic-Code-smtp-550-5-7-1/td-p/2035800

Re: SMTP error 550 5.7.1 part of network is on block list

TrevorP — Sat, 21 Feb 2026 10:04:34 GMT

Hi Leanne - PM duly sent.

Thank you,

Trevor

Re: SMTP error 550 5.7.1 part of network is on block list

TrevorP — Wed, 25 Feb 2026 09:43:06 GMT

@Leanne_T

Bit more information. Messages are now being rejected by nnnn@Outlook.com. This is a relatively recent occurrence, As of Feb 12th, it was working, now it's not.

best,

Trevor

Re: SMTP error 550 5.7.1 part of network is on block list

Ritu_D — Wed, 25 Feb 2026 09:52:49 GMT

Hi @TrevorP

Thank you for coming back to us on here with that information.

Outlook and Hotmail both work off Microsoft so it is possibly the reason why.

We have seen others with similar issues, we have sent off your examples to the relevant teams who can investigate this further.

Thank you for your patience.

Ritu

Re: SMTP error 550 5.7.1 part of network is on block list

matthew29 — Fri, 27 Feb 2026 20:20:51 GMT

I have just had a failure sending to any hotmail.com, hotmail.co.uk and live.com addresses

Final-recipient: rfc822; @XX@hotmail.com

Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [212.159.14.17] 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=11BCEBBEF940A923]

[AMS1EPF0000008D.eurprd05.prod.outlook.com 2026-02-27T19:59:41.988Z 08DE75DF7D8AD389]

Last-attempt-Date: Fri, 27 Feb 2026 19:59:42 +0000