Microsoft wins the inbox battle (for now)

If you have stopped by Spam Resource or Wombatmail recently, you might have noticed a few changes around here. It’s been updates on updates on updates recently. Updated design, templates, styling, code, cleaning up cruft left and right. And, also, updating the data shared over on Wombatmail.

That data refresh brings us right to the latest snapshot over on Wombatmail’s Ranking Mailbox Providers by MX page, calculating counts for where inbound mail goes for the top domains.

For the first time in a while, Microsoft has claimed the number one spot in our "ten million domains" dataset as the leading mailbox provider for business email, corporate and personal 1:1 mailbox domains.

To give some background on how this data works: I take the top ten million domains as ranked by host.io and parse their highest-priority MX records, collapsing specific hostnames down to their organizational domain (for instance, mapping microsoft-com.mail.protection.outlook.com to outlook.com). Out of those ten million domains, 4,774,590 publish a usable MX record, and when you roll up the org domain for all of those MX records, you end up here. While perhaps not a scientific methodology, it offers a fascinating snapshot into mailbox provider reach, helping us answer the question of who is powering inbound business email today.

And, today, Microsoft leads that charge. In the latest pull, Microsoft 365 (and Outlook.com) host mail for 734,305 domains (a 15.38% market share of domains with MX records), narrowly pulling ahead of Google Workspace (google.com), which comes in at 733,753 domains (15.37% share). That is a razor-thin margin of just 552 domains separating the two tech giants!

So, Microsoft wins the battle, but will they win the war?

Probably not, at least not permanently. The reality in this domain hosting race is that Microsoft and Google tend to swap places at the top periodically depending on when the dataset is pulled and how domain rankings shift. Together, though, they dominate: Microsoft and Google host mail for over 30% of all domains with active MX records in this dataset.

Further down the rankings, another interesting takeaway is the strong standing of Tencent QQ (qq.com). Holding the number four spot, Tencent hosts inbound mail for 60,110 domains (1.26% share). Given that Tencent’s services are primarily localized to China, it speaks to how many organizations there prefer keeping their email infrastructure in-country. While 60,000+ domains represents less than 10% of what Microsoft or Google host individually, it is still a massive number of business domains for a regional provider to command.

Beyond the top players, the remaining market is heavily fragmented across web hosts, regional ISPs, security gateways, and self-hosted infrastructure. Curious to dive deeper into the data? You can check out the full ranking of the top 5,000 providers and download the complete raw dataset over at Wombatmail.