But how can you possibly deliver email via IPv6 if their MX host doesn't have IPv6 address at all? $ host hotmail.com hotmail.com has address 204.79.19

But how can you possibly deliver email via IPv6 if their MX host doesn't have IPv6 address at all? $ host hotmail.com hotmail.com has address 204.79.197.212 hotmail.com mail is handled by 2 hotmail-com.olc.protection.outlook.com. $ host hotmail-com.olc.protection.outlook.com. hotmail-com.olc.protection.outlook.com has address 104.47.57.161 hotmail-com.olc.protection.outlook.com has address 104.47.58.161 On the other side, if a host announces that they have an IPv6 address - do you think they do it mostly for spamers? $ host gmail.com | grep handled | head -n1 gmail.com mail is handled by 5 gmail-smtp-in.l.google.com. $ host gmail-smtp-in.l.google.com. gmail-smtp-in.l.google.com has address 173.194.73.27 gmail-smtp-in.l.google.com has IPv6 address 2a00:1450:4010:c1c::1a