No-one likes spam specially HOTMAIL.
Personally, I’d rather HOTMAIL adopted the Gmail approach of moving suspected spam into a spam folder instead of rejecting the email.
In this case, HOTMAIL has determined my Internet Service Provider’s IP Address is blocked, not me or my IP address but the entire network.
My ISP is Optus (Australia) so effectively, HOTMAIL is blocking somewhere near 3million emails a day.
Rejected message
This is the mail system at host mail110.syd.optusnet.com.au.
I’m sorry to have to inform you that your message could not be delivered to one or more recipients. It’s attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system
<xxxxxxx@hotmail.com>: host hotmail-com.olc.protection.outlook.com[104.47.37.33] said: 550 5.7.1 Unfortunately, messages from [211.29.132.97] weren’t sent.
Please contact your Internet service provider since part of their network is on our blocklist (S3150).
You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.
[CY1NAM02FT009.eop-nam02.prod.protection.outlook.com] (in reply to MAIL FROM command)
Research
Google “Hotmail Blocklist (S3150)” ..
Optus network on Hotmail blocklist
The same issue was reported in December 2017 to Optus but it doesn’t look like anything has been done about it.
For what it’s worth I posted to Optus asking them to do something about it.
All I got back was that Optus technicians were unable to resolve the issue.
How to get an IP Address Unblocked?
Firstly, we are not connected with MxToolbox in any way.
Obviously, you can try delisting an IP yourself, but from experience, it isn’t easy. Go to the website that is blacklisting the address and follow the instructions.
MxToolBox
MxToolbox keeps your business running smoothly with tools that make your day-to-day work easier and monitoring solutions that give you peace of mind.
MxToolbox Experts can help you get delisted. All paid MxToolbox accounts come with access to our experienced support team, including helping to delist your IP addresses and domains from blacklists.
Good luck!