Finding the correct Inbound SMTP Host Address for an Office 365 (O365) domain is critical to proper email flow.
Host Address Pattern
The MX record does have a pattern but it is not a guarantee that the host address will always follow the pattern. Some of the common host address patterns are:
Finding the Correct Host Address from the Office 365 Admin Center
The Inbound SMTP Host Address for Office 365 domains should be the O365 MX record. It can be found in the Setup menu of the O365 Portal.
Verify and adjust the Inbound SMTP Host Address based on what is given by O365. Below is the domain DNS information screen provided in O365 that will be used to obtain the correct information.
Arrow 1: Usually you will see a note just below the domain name that indicates the domain's DNS is managed outside of O365. If you are integrated with GoDaddy to allow O365 to manage the DNS from this screen, you will see a different message.
Arrow 2: You will see a warning that DNS errors have been detected. That is normal because the MX record will be pointing to Mailprotector, not to the O365 recommended address. If you have not changed the MX record yet, this warning message may not be present.
Arrow 3: The Exchange Online section will display the MX record for the O365 domain. This is the address that needs to be entered into the Inbound SMTP Host Address setting in the Mailprotector Console. This address and the receive connector must be configured correctly to ensure mail flows as expected.