"I've only come across one domain that was using our IPv6 address to deliver mail to us, and it was an educational institute - go figure! - Many e-mail services, especially those that are targets of spam will be longer in rolling out mail…"
"your mx record should point to mail.desertpenguin.info with a not too short of a TTL. You should then be able to have an A and AAAA record entered for mail.desertpenguin.info - make sure they are the same TTL and of reasonable length (at least 4…"
"PC-1 is sending the return traffic/responses for PC-3 to the directly attached network - ie, to the network between PC-1 and PC-2 - instead of sending it to PC-2's address for further routing. furthermore, PC-2 would have the same IPv6 subnet…"
Welcome to gogoNET Tom! You may want to join the v6 in Ireland and v6 System Administrators groups. Also, you'll make better connections if you fill out the summary section of your profile. Bye for now... and don't forget to invite your IPv6 friends to join us.