We are using Icewarp and recently our users are unable to send email on any hotmail/Live account, on the other hand no problem appears in receiving email from hotmail ID.
Below is the returned mail response error
550 SC-001 (SNT0-MC4-F42) Unfortunately, messages from 174.12.x.x weren't sent. Please contact your Internet service provider since part of their network is on our block list
Any idea how to unblock our mail server IP ?