Email (not Plusnet email) problem

[#1]

I recently left Plusnet to join BT, however I wqas unable to send to any Hotamil addressses, so I returned to Pluse net. Sadly the fault is now here also. I have tried to get this resolved witha number of Software providers including Plusnet, but they all say it is someone elsed problem. 😞

I am running under Windows 10 using Mozilla Thunderbird.I have my own domain name registered with 123.reg, this means I can kee[p my email addresses when I move service provider. It has all worked fine in the past.. Here is the failure message I get:

    host hotmail-com.olc.protection.outlook.com [104.47.55.161]
    SMTP error from remote mail server after pipelined end of data:
    550 5.7.1 Unfortunately, messages from [79.170.44.40] 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. [BN8NAM12FT031.eop-nam12.prod.protection.outlook.com]

Reporting-MTA: dns; mail40.extendcp.co.uk

Action: failed
Final-Recipient: rfc822;xxxxx@hotmail.com
Status: 5.0.0
Remote-MTA: dns; hotmail-com.olc.protection.outlook.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [79.170.44.40] 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. [BN8NAM12FT031.eop-nam12.prod.protection.outlook.com]

If anyone can solve this or even point me in the right direction I would be oblidged.

Moderators Note: Personal information removed (email address)

[#2]

@JohnCT1  the mail server you are sending from ( it appears to be mail40.extendcp.co.uk ) is on the Sorbs blacklist. The microsoft mail server is refusing to accept mail from it because of that. Who provides the email service for your domain ? is it 123 reg or are they just the domain registrar ?

[#3]

Moderators Note

This topic has been moved from Everything else to Tech help

[#4]

They are not alone in being blocked. Just do a search regarding MS blocking legimate mail servers. All you can do is contact your host and get them to deal with MS direct. Of course, if it is a spam server then MS are probably right to block it. 

[#5]

Thanks you all for your replies. I must apolagise for the lateness of my reply, it has taken this long to get ti sorte, not resolved. It is nmot v=clear that it is insdees Ms blocking  the mai server. 

[#6]

You might be better off sending your outgoing mail via the Plusnet server (although that is not without its own problems).

Edit: Or was the 'not resolved' a typo for 'now resolved'?!