← All insights · Mon, 10 Aug 2026

Who runs the world's inboxes? MX market share across 50,000 domains

Google, Microsoft, self-hosted, and a very long tail. Why deliverability is hard.

We resolved the MX records of 50,000 of the most-linked domains (80.7% are mail-enabled) and classified who actually receives their mail:

Other / self-hosted, 32.5%
Google Workspace / Gmail, 28.2%
Microsoft 365 / Outlook, 22.7%
Proofpoint, 5.6%
Mimecast, 3.1%
Tencent QQ, 2%
Namecheap, 1.2%
Cisco IronPort, 0.9%

Google Workspace (28.2%) and Microsoft 365 (22.7%) anchor the market, but "Other / self-hosted" stays huge. That long tail is exactly why deliverability is hard: every provider greylists, rate-limits and reputation-scores differently. A sender that sails into Gmail can be throttled by a self-hosted Postfix or a Proofpoint gateway. Testing against real MX behavior, not assumptions, is the only way to know an address is actually reachable.

Free deliverability tools → Check any domain (MX, SPF, DMARC), test your own inbox placement scored out of 100, generate SPF and DMARC records, or run a blocklist check, all free with no signup and nothing stored, at deliverability.mailtester.ninja/tools.

Verify a real address → This is aggregate DNS data. To check whether a specific email address exists and is deliverable, use MailTester Ninja , real-time, nothing stored.

Data: MailTester Ninja Email Infrastructure Index, 50,000 domains, snapshot Mon, 10 Aug 2026 04:18:49 GMT. Reuse freely under CC BY 4.0.

FAQ

What is the most popular email provider?

In this sample, Google Workspace / Gmail leads at 28.2% of mail-enabled domains, followed by Microsoft 365 / Outlook at 22.7%.

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