reverse dns configuration for IPV4, IPV6+ dns+ mail ?

[Reindl Harald]

Am 19.06.2017 um 08:49 schrieb Matus UHLAR - fantomas:
>>> On 18.06.17 16:26, Mark Elkins wrote:
>>>> Put two reverse records in both  the IPv4 and IPv6 reverse zones....
>>>>
>>>> in the "125.124.123.in-addr.arpa" zone:
>>>>
>>>> 126   IN   PTR   mail.xxx.com.
>>>> 126   IN   PTR   ns.xxx.com.
> 
>> Am 18.06.2017 um 17:38 schrieb Matus UHLAR - fantomas:
>>> there are cases when having two reverse records is misleading
> 
> On 19.06.17 01:05, Reindl Harald wrote:
>> it's nearly always misleading and results in randomness on the 
>> receiving server which name get logged and if A/PTR matches
>>
>> normally you should always have:
>>
>> * IP with *one* PTR
>> * the A-Record for the PTR matches
>> * smtp_helo_name of your MTA matches the same name
> 
> Even this is not required. In fact, requiring this breaks SMTP RFC.
> The only requirement on helo name is that host must exist and be canonical,
> which means it has to point to A or AAAA record

should != required
it's best practice

anyways, with 2 PTR records for the same IP on servers with 
http://www.postfix.org/postconf.5.html#reject_unknown_client_hostname 
you play lottery because one time it's logged as unknown and the other 
time as matching, the unknown cases would trigger 
reject_unknown_client_hostname