I just tested sending emails to hotmail accounts and received the same error message "
hotmail-com.olc.protection.outlook.com[184.108.40.206] said: 550 5.7.1
Unfortunately, messages from [220.127.116.11] 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
[DB8EUR05FT016.eop-eur05.prod.protection.outlook.com] (in reply to MAIL