The mail setup for this forum is somewhat broken:
1.
The sending ip 2602:fc62:a:1003:216:3eff:fea3:3fe is not included in the SPF record:
% host -t txt discuss.linuxcontainers.org
discuss.linuxcontainers.org descriptive text "v=spf1 redirect=_spf.stgraber.org"
% host -t txt _spf.stgraber.org
_spf.stgraber.org descriptive text "v=spf1 ip4:45.45.148.0 ip6:2602:fd23:8:1001:216:3eff:feb3:6927 ip6:2602:fd23:8:1002:216:3eff:fe9a:b0f9 ip6:2602:fd23:8:1003:216:3eff:fea3:3fe include:_spf.google.com ~all"
2.
There is a typo in the PTR record for 2602:fc62:a:1003:216:3eff:fea3:3fe
% host 2602:fc62:a:1003:216:3eff:fea3:3fe
e.f.3.0.3.a.e.f.f.f.e.3.6.1.2.0.3.0.0.1.a.0.0.0.2.6.c.f.2.0.6.2.ip6.arpa domain name pointer postifx03.core.dcmtl.stgraber.net.
This should probably be postfix03.