[marcus0x62]

You like to make absolute statements like “always”, but I know of large organizations (Fortune 500) that use Proofpoint, but not Microsoft email security. And in endpoint, there are shops that license defender as part of an EA, but don’t use it - of course, those seats go into the Forrester figures that Microsoft likes to tout.

[FreakLegion]

Sure, I can enumerate the handful of the Fortune 500 that don't use Microsoft. Palo Alto Networks, for example, has TAP sitting in front of Google. In PANW's case it's because of a broader partnership Nikesh put together with Google in 2018, which also involved moving from AWS to GCP. This is stupendously uncommon, though.

If you were to look through the System -> Inbound Mail settings for every PPS customer, you'd find a sea of x.mail.protection.outlook.com, some on-prem Exchange servers, and practically nothing else. I'm comfortable with "always" as a description of this state of affairs, but you do you.