Why would an organization use an SEG if they use Outlook or Gmail?

Perhaps this is a silly question, but I’ll ask it anyways. I am under the impression that companies as big as MS and Google would already have robust malicious email detection capabilities, thereby making any independent secure email gateways redundant. And yet, in my new position see that they’re quite popular with clients despite using Outlook and Gmail.

Can someone educate me on what SEGs such as Barracuda, Mimecast, and Proofpoint are doing that MS and Google aren’t? I would’ve …

big capabilities companies cybersecurity detection email gmail google making malicious organization outlook question secure email secure email gateways seg under