This is helpful to someone who's trying to obtain/maintain visibility into the email hosting vendor associated with a domain. This is a good Metric for QBRs, recurring site reviews, and an onboarding report. Also, if your MSP resells M365, this Metric can be used to create a cross customer report/onboarding report to audit if their email hosting vendor is M365 or not, so that, if not, you can mention that you can sell them licenses to M365.

SystemInfo.EmailHostingVendor