MailTester Ninja← All insights · Sat, 11 Jul 2026
Google runs IPv6 on 100% of its inboxes, Microsoft on 91.3%. Take those two out and IPv6 email adoption collapses to 12.9%.
Everyone says "IPv6 is here." For the web, mostly true. For email, it is a mirage.
We resolved the MX records of 50,000 of the most-linked domains and checked whether any of their mail servers publish an AAAA record, meaning they can actually receive over IPv6. No sending, no personal data, just DNS.
55.2% of mail-enabled domains have at least one IPv6-capable MX. That sounds healthy. It is not, because two companies carry almost the whole number:
| Email provider | IPv6 MX |
|---|---|
| Other / self-hosted | ██░░░░░░░░ 18.4% |
| Google Workspace / Gmail | ██████████ 100% |
| Microsoft 365 / Outlook | █████████░ 91.3% |
| Proofpoint | ░░░░░░░░░░ 0.6% |
| Mimecast | ░░░░░░░░░░ 0% |
| Tencent QQ | ░░░░░░░░░░ 4.2% |
| Namecheap | ░░░░░░░░░░ 0.2% |
| Cisco IronPort | ░░░░░░░░░░ 4.5% |
| Zoho | ░░░░░░░░░░ 0% |
| Barracuda | ░░░░░░░░░░ 0% |
Google (100%) and Microsoft (91.3%) run IPv6 on nearly every inbox. Remove those two, the providers that already anchor most of the world's mail, and IPv6 email adoption falls from 55.2% to 12.9%. The enterprise security gateways that gate corporate mail, such as Proofpoint, Mimecast and Barracuda, are effectively not on IPv6 at all.
Why it matters for deliverability. IPv6-only sending is a dead end. It reaches Gmail and Outlook and little else. Dual-stack is not optional. IPv4 is still the backbone of email, and that is where blocklists, FCrDNS and IP reputation are mature. The takeaway: IPv6 email is not adopted. Google and Microsoft adopted it for you. Plan your sending for an IPv4 world with two big IPv6 exceptions.
Data: MailTester Ninja Email Infrastructure Index, 50,000 domains, snapshot Sat, 11 Jul 2026 12:39:35 GMT. Reuse freely under CC BY 4.0.
In this 50,000-domain sample, 55.2% of mail-enabled domains have at least one MX with an IPv6 (AAAA) record. Excluding Google and Microsoft it drops to 12.9%.
Only dual-stack. IPv6-only sending reaches Gmail and Outlook but almost nothing else, because most providers, especially security gateways like Proofpoint and Mimecast, have no IPv6 MX. Keep IPv4 as the primary path.