We are aware that Microsoft is currently blocking some email delivery from our shared hosting email relays to some of their email services including Hotmail.com and Outlook.com
We are working to resolve this issue by addressing the cause of the blocks and we are adding more email relay servers. We are also in contact with Microsoft, requesting they remove the blocks and provide more information on what is causing the blocking.
In general though the cause of these blocks is mail identified as SPAM that is sent from our relay servers. This includes forwarded SPAM where email accounts have forwarding enabled, fraud accounts, contact forms being abused and compromised email accounts sending SPAM.
Customers should ensure their contact forms have a captcha to stop abuse and forwarding is removed from email accounts that are receiving SPAM.
Our Business email product and Office365 are NOT affected by these issues, for more details on Business email please see https://www.blacknight.com/office365/ and https://www.blacknight.com/business-email/