Part of Plusnet internet provider service blocked at outlook.com?

[#1]

I have been working for a client with an outlook.com email address and for the last 4 days my emails to him are being bounce back. The bounced email says it's a permanent error and my internet provider is having some parts of its service blocked. See below in red please. Any help much appreciated.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

blablabla6@outlook.com
   host outlook-com.olc.protection.outlook.com [104.47.12.33]
   SMTP error from remote mail server after pipelined sending data block:
   550 5.7.1 Unfortunately, messages from [79.170.40.142] 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. [DB3EUR04FT050.eop-eur04.prod.protection.outlook.com]
Reporting-MTA: dns; mail142.extendcp.co.uk

Action: failed
Final-Recipient: rfc822;blablabla@outlook.com
Status: 5.0.0
Remote-MTA: dns; outlook-com.olc.protection.outlook.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [79.170.40.142] 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. [DB3EUR04FT050.eop-eur04.prod.protection.outlook.com]
Return-path: <blablabla@hfdesign.net>
Received: from 76.115.115.87.dyn.plus.net ([87.115.115.76] helo=[192.168.1.19])
    by mail142.extendcp.co.uk with esmtpsa (TLSv1:ECDHE-RSA-AES256-SHA:256)
    (Exim 4.92)
    id 1hSevj-0003Ya-Sr
    for blablabla@outlook.com; Mon, 20 May 2019 10:50:07 +0100
From: blablabla <blablabla@hfdesign.net>
Content-Type: multipart/alternative; boundary="Apple-Mail=_65A80991-270C-4D52-8375-3684A256CB1C"
Message-Id: <307F8038-562E-4BF6-B371-E3378F77E9DC@hfdesign.net>
Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\))
Subject: Re: ETLT
Date: Mon, 20 May 2019 10:50:03 +0100
References: <DB6PR0402MB2760D7B2CC94A3FDC3BC9712A42B0@DB6PR0402MB2760.eurprd04.prod.outlook.com> <46CEFCC7-F087-4DAF-B0A0-D1ACF96AA477@hfdesign.net> <DB6PR0402MB276050A4C17ABF87AA46E281A4200@DB6PR0402MB2760.eurprd04.prod.outlook.com> <E8A29928-A03E-415F-8CD3-7012E0B66B3E@hfdesign.net> <DB6PR0402MB27603060A94189A2968F4EB2A4200@DB6PR0402MB2760.eurprd04.prod.outlook.com> <240EC362-0BCC-4F09-9EA3-2A07A56E4A16@hfdesign.net> <DB6PR0402MB2760DCD1068A582D97C447E9A4390@DB6PR0402MB2760.eurprd04.prod.outlook.com> <F71AA451-713A-4928-87ED-4DAFA1063A62@hfdesign.net> <DB6PR0402MB2760A41BBB94172A3DC389F0A4390@DB6PR0402MB2760.eurprd04.prod.outlook.com> <256AD42D-08B6-4E8C-B2D8-AD48FE7A5315@hfdesign.net> <DB6PR0402MB2760447814F9EE964C4696D3A4390@DB6PR0402MB2760.eurprd04.prod.outlook.com> <9C67DA46-E151-40F1-99AB-07E246A1B9ED@hfdesign.net> <DB6PR0402MB27604B1CDD7C517816EADC4EA43A0@DB6PR0402MB2760.eurprd04.prod.outlook.com> <EF46DCDB-8E36-4488-BA07-A4514E628996@hfdesign.net> <DB6PR0402MB2760E6172E06A240A124968EA43A0@DB6PR0402MB2760.eurprd04.prod.outlook.com> <FAD4054F-65B4-4673-8796-5392849950D2@hfdesign.net> <DB6PR0402MB2760B4CF755946B71CF37D2EA43B0@DB6PR0402MB2760.eurprd04.prod.outlook.com> <EE799F3D-0DFC-473E-8A89-9CC726519A62@hfdesign.net> <DB6PR0402MB2760999741CC9CCC14AB4DFEA43B0@DB6PR0402MB2760.eurprd04.prod.outlook.com> <C8AC3860-2600-4CC2-BF52-8FA0A60D53A7@hfdesign.net> <DB6PR0402MB27602891034E175002AF390EA4360@DB6PR0402MB2760.eurprd04.prod.outlook.com> <F5BC0482-5E65-4637-BBB7-31FD3D261D47@hfdesign.net> <DB6PR0402MB27604A6D6689F9161554099CA4370@DB6PR0402MB2760.eurprd04.prod.outlook.com> <6AF4CE62-BDE7-4DF2-8EB0-4651AC0BDD9E@hfdesign.net> <DB6PR0402MB2760C1C373C4F2C7056D639DA4310@DB6PR0402MB2760.eurprd04.prod.outlook.com> <CFAF92ED-F52B-40FE-9597-5CC9BF845E28@hfdesign.net> <DB6PR0402MB2760795B24517FFB9EE528ACA40B0@DB6PR0402MB2760.eurprd04.prod.outlook.com> <1299A59A-50A8-474F-9250-5D20A6C7701A@hfdesign.net> <DB6PR0402MB276054936C2C33F135A11EAAA4040@DB6PR0402MB2760.eurprd04.prod.outlook.com>
To: blablabla <blablabla@outlook.com>
In-Reply-To: <DB6PR0402MB276054936C2C33F135A11EAAA4040@DB6PR0402MB2760.eurprd04.prod.outlook.com>
X-Mailer: Apple Mail (2.3124)
X-Spam-Score: 0.0
X-Exim-DSN-Information: Due to administrative limits only headers are returned

[#2]

It looks like your email is being sent via mail142.extendcp.co.uk  rather than the PN mail servers. It seems like whatever that is , it's on a blacklist.

[#3]

Okay thanks MrW. I have my own domain and hosting so use my domain's mail servers. Does that mean it's that rather than PN?

[#4 · Accepted solution]

Yes, you need to get  whoever hosts your domain to get their mail server off whatever blocklist outlook thinks it's on.

It doesn't appear to be anything to do with PN.

[#5]

Very helpful thanks MrW.

[#6]

Do you have an spf record on your domain ? Not having an spf record that allows sending from the mail server in question is becoming a common reason for non-delivery of email

[#7]

Er, don't know. I will have to check on this MrW. I am in contact with my hosting provider to find out. Thanks for the tip squire.

[#8]

The problem has been sorted by changing the outgoing mail server in my client from mail.mydomain.com to mail54.extendcp.co.uk. It's a problem that has never occurred before but it's fixed now. I think before mail out was using mail142.extendcp.co.uk though my domain.

Thanks to all who helped, much appreciated.