Outlook.office365.com Error message

I have recently got the following error message from eM Client:

eM Client can’t verify identity of “Outlook.office365.com”. The host name doesn’t match the name specified in the certificate. You might be connecting to a server that is pretending to be “outlook.office365.com” which could put your confidential information at risk.

I also got a similar message while watching YouTube videos. It was something like “can’t verify the certificate and Do you want to connect to the server or not|”  but I can’t remember and I missed to write down the exact message.

A BT engineer came recently in my place to transfer the BT master phone socket to another room (I live in a share accommodation). After that visit I connect to the internet wirelessly (I used to connect to internet wired). Also there is not a microfilter between the master socket and the router (as it was before the visit of the BT engineer). I don’t know if these changes made by the BT engineer affected my internet connection and that resulted in the above error messages.  


This message can be caused by incorrect hostname or because information in certificate differs from information in your account,
please try to change hostname or change certificate on server.
Let me know if this helped.

Kind regards