Determining that a domain is using Office 365 via mx records

Question

We are trying to detect that a new signup is or is not using Office 365 based off of their email address.

It's easy to identify the mx record domains used for Office 365 "UNIQUE_TOKEN.mail.protection.outlook.com", so searching for ' .mail.protection.outlook.com ' seems like the thing to do.

Question: are there other "Exchange Online" services that use this MX record format that are NOT Office 365?

I think that Office 365 inherited this MX record schema from other services, and that there could still be some other services that actively use it. But I'm having a hard time confirming it.

Answer 1

You can tell if the user is using o365 email account or not by using this format: MyEmailId@MyTenantName.onmicrosoft.com. So you should use *.onmicrosoft.com which tells you the user is a o365 user which uses Exchange online. All other online Microsoft services uses exchange online. for example: MS Dynamics crm uses exchange online for all its authentication services. hope this helps.