[FreakLegion]

Silicon Valley in particular uses Google Workspace at a much higher rate than the rest of the world. If you count every one- or two-person startup as a company, Google probably does have a solid majority. If you count mailboxes, Microsoft still easily wins.

Note that MX records are misleading here. They have no false positives, but are full of false negatives --- daisy-chaining MTAs is common, and since Microsoft owns the mailbox, it's invariably last in the chain. So the MX record will show something like Proofpoint (pphosted) or Mimecast or an internal company host, when really it's Microsoft in the end.