Currently as only a handful of providers even support receiving IPv6 mail and due to spammers still using IPv4, we don't know yet. Usually /64 is considered for

Currently as only a handful of providers even support receiving IPv6 mail and due to spammers still using IPv4, we don't know yet. Usually /64 is considered for reputation in abuseipdb. Another fact is gmail which supports IPv6 requires a PTR pointing back to the domain the mail is sending.[1] Currently a lot of providers which gives IPv6 does not support adding PTR records for IPv6, because it is handled differently than IPv4. This has led to lot of people defaulting to IPv4 when sending mail.[2] [1] https://support.google.com/mail/answer/81126 https://support.google.com/mail/answer/81126 [2] https://google.com/search?q=ipv6+gmail+ptr https://google.com/search?q=ipv6+gmail+ptr