The email server has been placed in Hotmail.com/Live.com/Outlook.com block list. Users with email addresses with these domains, temporary will not receive emails from Mojo Helpdesk.
We have submitted an official delisting request, and waiting for the Microsoft support team to respond.
Apologies for any inconvenience, and thank you for your continued support. If you have any further concerns or questions, please do not hesitate to reply to this message.
Microsoft finally answered that they mitigated the issue:
Thank you for contacting the Outlook.com Deliverability Support Team.
We have implemented mitigation for your IP [220.127.116.11] and this process may take 24 - 48 hours to replicate completely throughout our system.
Outlook.com Deliverability Support
Privacy Statement .
One Microsoft Way
Redmond, WA 98052 USA
This should resolve the issue.