We are aware of an issue that is preventing email from being sent to @hotmail.com and @live.com recipients. When sending an email to one of these domains, you may receive an email from “Mail Delivery System” with the subject “Mail delivery failed: returning message to sender” with the following message:
host mx4.hotmail.com [18.104.22.168]: 550 SC-001 (SNT0-MC2-F50) Unfortunately, messages from **.**.***.*** weren't sent. Please contact your Internet service provider since part of their network is on our block list. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors.
We are working hard to resolve this issue and we will keep you posted on any progress.
We apologize for any inconvenience this issue may cause.