One question: Mar 23 07:08:35 mail named[544]: network unreachable resolving 'star.c10r.facebook.com/AAAA/IN': 2a03:2880:f1fd:b:face:b00c:0:99#53 Mar 23 07:08:35 mail named[544]: network unreachable resolving 'star.c10r.facebook.com/A/IN': 2a03:2880:f1fd:b:face:b00c:0:99#53 Mar 23 07:08:35 mail named[544]: network unreachable resolving 'star.c10r.facebook.com/AAAA/IN': 2a03:2880:f0fc:b:face:b00c:0:99#53 Mar 23 07:08:35 mail named[544]: network unreachable resolving 'star.c10r.facebook.com/A/IN': 2a03:2880:f0fc:b:face:b00c:0:99#53 Mar 23 07:08:35 mail named[544]: network unreachable resolving 'star.c10r.facebook.com/AAAA/IN': 2a03:2880:f1fc:b:face:b00c:0:99#53 Mar 23 07:08:35 mail named[544]: network unreachable resolving 'star.c10r.facebook.com/A/IN': 2a03:2880:f1fc:b:face:b00c:0:99#53 Mar 23 07:08:35 mail named[544]: network unreachable resolving 'star.c10r.facebook.com/AAAA/IN': 2a03:2880:f0fd:b:face:b00c:0:99#53 Mar 23 07:08:35 mail named[544]: network unreachable resolving 'star.c10r.facebook.com/A/IN': 2a03:2880:f0fd:b:face:b00c:0:99#53 Ports are open 53 for incoming/outgoing traffic. I read in other topic you can ignore this or disable IPV6 at all.