Well done for first steps. Even (one of) mail servers' IPv6 record has a valid reverse record, very nice! Now, how about adding reverse to the main AAAA too?

Well done for first steps. Even (one of) mail servers' IPv6 record has a valid reverse record, very nice! Now, how about adding reverse to the main AAAA too? Also, what's up with one of MX'es lacking IPv6 address? With both mail.linkedin.com and mail-c.linkedin.com having the same priority (10), that's a recipe for 50% of delivery attempts randomly failing to IPv4. $ dig +short aaaa linkedin.com 2620:109:c002::6cae:a0a $ dig +short -x 2620:109:c002::6cae:a0a (no reply) $ dig +short mx linkedin.com 10 mail-c.linkedin.com. 10 mail.linkedin.com. $ for i in mail.linkedin.com. mail-c.linkedin.com.; \ do echo $i; dig +short aaaa $i; done mail.linkedin.com. (no reply) mail-c.linkedin.com. 2620:109:c006:104::215 $ dig +short -x 2620:109:c006:104::215 mail-c.linkedin.com.