Plusnet SMTP IP 212.159.14.17 blocklisted by Microsoft (S3140) – needs delisting

[#1]

I am sending email via Plusnet’s SMTP servers. The sending IP shown in the
Microsoft bounce is 212.159.14.17, which resolves to avasout03.plus.net and
belongs to Plusnet Plc (AS6871). Microsoft has blocklisted this IP with error
S3140. Because this is a Plusnet-owned outbound mail server, only Plusnet can
request delisting via Microsoft SNDS/JMRP. Please escalate this to the email
platform team for investigation and delisting.

[#2]

This problem has being going on for weeks.  The main (but not the only) topic about is this one:

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

[#3]

Thanks.  I have raised a complaint/question with Plusnet.

[#4]

We're really sorry this is an ongoing issue, I can assure you it's been raised with Microsoft. 

[#5]

@plusnettony  @MisterW 

A couple of days ago, on another thread, I wrote:

"I gather that even after migration to Greenby, outgoing email is going via Plusnet’s servers for the foreseeable future. Is this because Greenby don’t have servers available or they are declining to deploy them for fear of them immediately becoming blocklisted due to the ongoing problems that, for once, are not of their making?".

At least, that's how it appears to me. Would either of you be able to provide definitive statements on the points raised?

[#6]

Outbound email will move to Greenby at a later date. The timing is our decision, but there are a few complexities on our side that we need to work through first to avoid causing issues for some users. We’ll share more updates as soon as we’re ready to make the switch.

[#7]

@plusnettony 

Can you confirm that this represents the current pre and post migration status as currently planned 

[#8]

Essentially, yes.

[#9]

@plusnettony wrote

Outbound email will move to Greenby at a later date.

Does this apply to all brands?

I seem to remember reading somwhere that Force9 had already moved output to Greenby?

[#10]

Some have been done, some not. The answer above specifically refers to relay.plus.net.

Eventually, all will be migrated to Greenby. 

[#11]

Received this via email today:

Thank you for your ongoing patience.

Whilst it's not yet fully resolved, improvement has been made and outbound emails to Microsoft addresses do appear to now be working to greater extent. We continue to work with Microsoft for a full resolution. 

Should you continue to experience the problem from today (27/03) please receive examples of the email headers related to the issue. 

Should I not hear back by 02/04 I will work on the basis that the matter is resolved for you.

Kind regards,

Matt Sladden

[#12]

Got through to msn.com contacts last night for the first time in months. Let's hope the Microsoft door stays open permanently to Plusnet/Greenby servers.

[#13]

So much for that.  My emails to hotmail addresses are being rejected again.  Plusnet's closing response to my complaint said that my service had been moved to Greenby, but I've not had any notification from Greenby.  Have complained again to Plusnet.

[#14]

...But are your emails being sent by a Greenby host, or via existing Plusnet hosts - for now? I don't know.

So, what's occurring?

Well here is one I successfully sent earlier (to myself @ BT Email) via the Greenby Webmail service:
(IP address 213.5.176.224 is Greenby - https://www.whois.com/whois/213.5.176.224)

Authentication-Results: btinternet.com;
dmarc=pass header.from=<PN Username>.plus.com;
dkim=none;
spf=none smtp.helo=demian.gateway.enmail.co;
spf=pass smtp.mailfrom=<PN Username>.plus.com;
arc=none smtp.remote-ip=213.5.176.224
X-OWM-SPF-MAILFROM: Pass
X-OWM-SPF: 0

Received-SPF: none (btprdrgi040.btinternet.com: domain
demian.gateway.enmail.co does not designate permitted sender hosts)
identity=helo; receiver=btprdrgi040.btinternet.com; client-ip=213.5.176.224;
helo=demian.gateway.enmail.co;
Received-SPF: pass (btprdrgi040.btinternet.com: domain <PN Username>.plus.com
designates 213.5.176.224 as permitted sender) identity=mailfrom;
receiver=btprdrgi040.btinternet.com; client-ip=213.5.176.224;
envelope-from=<PN Email>@<PN Username>.plus.com; helo=demian.gateway.enmail.co;

X-Originating-IP: [213.5.176.224]
X-OWM-Source-IP: 213.5.176.224
X-OWM-Env-Sender: <PN Email>@<PN Username>.plus.com
X-SNCR-Rigid: 697AF6A81BCB7E76
X-OWM-DMARC-DOM: plus.com
X-OWM-DMARC: spf 0 dkim 7
X-OWM-DKIM: 5
X-VadeSecure-score: verdict=clean score=0/320, class=clean
X-SNCR-VADESECURE: CLEAN
X-RazorGate-Vade: Zzzzz.............................................!
X-RazorGate-Vade-Verdict: clean 0
X-RazorGate-Vade-Classification: clean

Received: from demian.gateway.enmail.co (213.5.176.224) by btprdrgi040.btinternet.com
id 697AF6A81BCB7E76 for ******@******.com; Sun, 5 Apr 2026 09:52:12 +0100
Received: from mail.enmail.co (unknown [91.204.208.8])
by gateway1.enmail.co (Postfix) with ESMTPS id EBF3D41B46
for <******@******.com>; Sun, 5 Apr 2026 08:52:11 +0000 (UTC)
Received: from mail.enmail.co (localhost [127.0.0.1])
by mail.enmail.co (Postfix) with ESMTP id BA3E1C0788
for <******@******.com>; Sun, 5 Apr 2026 08:52:11 +0000 (UTC)
Received: from webmail.greenby.com (192-168-116-62.hostns-roundcube.enmail-prod.svc.cluster.local 
[192.168.116.62])
by mail.enmail.co (Postfix) with ESMTPA id 8E070C06E5
for <******@******.com>; Sun, 5 Apr 2026 08:52:11 +0000 (UTC)
MIME-Version: 1.0
Date: Sun, 05 Apr 2026 09:52:11 +0100
From: "******" <PN Email@PN Username.plus.com>
To: ******@******.com
Subject: Route Test -  

BTW, IP address 212.159.14.17 is a Plusnet host: Whois IP 212.159.14.17

[#15]

My understanding is that if you use Greenby webmail, your outgoing messages will go through their servers i.e. mail.enmail.co whereas if you are using a client (e.g. MS Outlook), your outgoing messages are routed according to what you set up in the client. The expectation (i.e. official recommendation) is that relay.plus.net (which translates to 212.159.14.17 amongst others) is used but there's nothing to stop you specifying mail.enmail.co instead.