It seems that hotmail.com mail server sitting at hotmail-com.olc.protection.outlook.com
How often do you send messages to (mailbox)@hotmail-com.olc.protection.outlook.com?
Where did you get hotmail-com.olc.protection.outlook.com from?
The certificate needs to match the MX record for the domain. When I check:
> set type=MX
It's currently fixed (2020-01-11), Certificate chain is valid:
mail.protection.outlook.com 128 days remaining / 2048 bit
GlobalSign Organization Validation CA - SHA256 - G3 2062 days
remaining / 2048 bit / sha256WithRSAEncryption
GlobalSign Root CA (Certificate is self-signed.) 2939 days
remaining / ...