How long did you let it propagate?
[carl@mars ~]$ dig mx ipv6.port111.com
; <<>> DiG 9.6.2-P2 <<>> mx ipv6.port111.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 32953
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; QUESTION SECTION:
;ipv6.port111.com. IN MX
;; ANSWER SECTION:
ipv6.port111.com. 3575 IN MX 10 ipv6.port111.com.
;; ADDITIONAL SECTION:
ipv6.port111.com. 3593 IN AAAA 2001:470:7:78d::2
;; Query time: 123 msec
;; SERVER: 2001:470:c27d:e000:41bd:d9bf:9b66:9b95#53(2001:470:c27d:e000:41bd:d9bf:9b66:9b95)
;; WHEN: Sun Oct 10 17:52:28 2010
;; MSG SIZE rcvd: 78
HE seems to know about it too
[carl@mars ~]$ dig mx ipv6.port111.com @2001:470:200::2
; <<>> DiG 9.6.2-P2 <<>> mx ipv6.port111.com @2001:470:200::2
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1389
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; QUESTION SECTION:
;ipv6.port111.com. IN MX
;; ANSWER SECTION:
ipv6.port111.com. 3600 IN MX 10 ipv6.port111.com.
;; ADDITIONAL SECTION:
ipv6.port111.com. 3600 IN AAAA 2001:470:7:78d::2
;; Query time: 97 msec
;; SERVER: 2001:470:200::2#53(2001:470:200::2)
;; WHEN: Sun Oct 10 17:53:09 2010
;; MSG SIZE rcvd: 78