The IPv6 email mirage: 55.2% of MX "support" it, but two companies carry the entire story

The IPv6 email mirage: 55.2% of MX "support" it, but two companies carry the entire story

By the team at MailTester Ninja - a real-time email verification API that stores nothing.

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:

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.

Check any domain yourself - our free deliverability analyzer shows a domain's MX / SPF / DMARC in one click (no signup, nothing stored). Need to confirm whether a specific mailbox actually exists and is deliverable? That is exactly what MailTester Ninja's email verifier does in real time - and we store no data.

Source: MailTester Ninja's open Email Infrastructure Index - a live DNS scan of 50,000 of the world's most-linked domains, updated daily, aggregate only. Free to cite under CC BY 4.0. Snapshot: Sat, 11 Jul 2026 12:39:35 GMT.