Notices by Jan Schaumann (jschauma@mstdn.social), page 2

But all that is for _all_ gTLD domains, which includes millions of parked domains, typo-squatting and spam domains, etc.

What if we look at the Top 1M domains?

Let's pull the list from https://tranco-list.eu/...

For those 1 million domains, we find around 433K distinct MX servers in 230K domains. The top 20 mail server domains there are:

Google and Microsoft together handle over 60% of the Top 1M domains' mails!

Many other domains use service provides such as Proofpoint, Barracuda Networks, or Cisco / IronPort, but those may of course only sit in front of Google and Microsoft's mail servers as well.