2620:0:861:1::2 resolves to lists.wikimedia.org, but lists.wikimedia.org has not this IPv6-adress-entry.
Following some log-lines from my mail-server:
--snip---
Nov 9 22:07:54 platon postfix/smtpd[8917]: warning: 2620:0:861:1::2: address not listed for hostname lists.wikimedia.org
Nov 9 22:07:54 platon postfix/smtpd[8917]: connect from unknown[2620:0:861:1::2]
Nov 9 22:07:54 platon postfix/smtpd[8917]: 6CE95AFB1E: client=unknown[2620:0:861:1::2]
--snap---

and from host:
--snip---
00:29:24dab@dabpc:~$ host 2620:0:861:1::2
2.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.0.0.0.1.6.8.0.0.0.0.0.0.2.6.2.ip6.arpa domain name pointer lists.wikimedia.org.
00:31:39dab@dabpc:~$ host lists.wikimedia.org
lists.wikimedia.org has address 208.80.154.4
lists.wikimedia.org mail is handled by 60 mchenry.wikimedia.org.
lists.wikimedia.org mail is handled by 10 lists.wikimedia.org.

--snap---

I hope that help you to fix this little problem.

Sincerely,
DaB.

Version: wmf-deployment
Severity: minor
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=22028