On 19/11/2025 01:17, Matus UHLAR - fantomas via Postfix-users wrote:
In summary: Your IP address should resolve to $myhostname (via a DNS
PTR record), which in turn should resolve back to your IP (A and/or
AAAA record).
Not necessarily the $myhostname,
$myhostname is a bit of a simplification, and not strictly true.
but it should:
- resolve the IP to hostname that resolves back to the IP
Yes, but there's nore to it than that.
- the hostname should not be generic
(mail servers often refuse hostnames containing text "dynamic" or
format 11-22-33-44.example.net)
More specifically the PTR record should not be generic.
Further the $smtp_helo_name (which defaults to $myshostname) should
resolve to an IP (not necessarily the outgoing IP but it's most logical).
Yes, it necessarily needs to resolve to the same IP as the one used to
connect with or it doesn't satisfy FCRDNS. It can also resolve to other
IP addresses (via multiple A/AAAA records) but I tend to want to keep it
simple, no need risking that a bad implementation will only check one of
those records and reject for FCRDNS based on it checking the wrong one.
Further to this it is not strictly necessary that the HELO name matches
the hostname for the PTR record, but again, because bad implementations
do exist, I find it best to make sure it does, it falls under the
category of "why tempt faite?".
On 18.11.25 10:17, lejeczek via Postfix-users wrote:
Certainly no PTR record for my IP but - do ISPes even do that - for us
at home or in general customers anywhere, as opposed to co-located/
hosted stuff? (or registrars who can, who do reverse too?)
I'm not going to move home there to such ISP's area, but sincere
question, just out of curiosity.
It is generally not a good idea to attempt to host a mailserver on a
residential IP address, especially a dynamic one. If you do then you
will need to use a relayhost.
I read somewhere that 'hosts' locally, of such a private postfix might
play a role - when /hosts resolve/**to *localhost* (first or only) and
then postfix might send/use that - I don't remember details, if that
was a valid issue at all, but..
even then, is is only this time so for, in a couple years, when I got
FCrDNS, so should not be my postfix/setup.
There is nothing that you can do in your local hosts file to fix this
issue. Remote servers do not see your local hosts file and will not
check it.
Peter
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