What is an AAAA record?
An AAAA record maps a host name to an IPv6 address, the 128-bit successor to IPv4 (RFC 3596). A server with both an A and an AAAA record can be reached over either. For mail this matters twice: MX hosts with AAAA records receive over IPv6, and a sending server with IPv6 may send over it.
Reading the result
Addresses come with their TTLs and any CNAME chain. For each IPv6 address (up to four), the tool looks up its PTR record and checks that the PTR’s name points back to the same address, which Google requires of every sending IP. Then each of the domain’s first four MX hosts is checked for an IPv6 address.
Beat runs on the same engine, on a schedule, across all 41 checks and 25 blacklists. What it adds is asking again, noticing when an answer changes and telling you what to do about it.
Common problems it finds
IPv6 sending with no PTR
Google’s sender guidelines require a PTR for the sending address that resolves back to it. A server that starts sending over IPv6 without one gets 550 5.7.1 from Gmail, even when its IPv4 setup is complete.
A PTR that does not point back
The PTR’s host name must have an AAAA record holding the same address. Anyone can set a PTR to any name, so receivers check the round trip.
SPF that covers only IPv4
Mail sent over IPv6 is checked against the record’s ip6 terms. With only ip4 terms, it fails SPF, and Microsoft 365 turns away mail arriving over IPv6 that passes neither SPF nor DKIM.