Re: Ptr DNS and domains

[Viktor Dukhovni]

> On May 9, 2018, at 12:11 PM, Tobias Koeck  wrote:
> 
>> Publish exactly one primary name for each IP address via a single PTR record.
>  
> Sounds great but doesn't that mean I need exactly one unique public IP for 
> every domain? If I 'skip' the PTR records completely how likely is emails 
> will be bounced back?

No.  All it means is that each IP address reverse maps to one name.  No more, 
no less.
This has nothing to do with the domains you receive mail for, or whose mail you 
route
outbound.

-- 
Viktor.

Re: Ptr DNS and domains

[Tobias Koeck]

On Wed, May 9, 2018 at 5:59 PM, Viktor Dukhovni 
wrote:

>
> >
>Publish exactly one primary name for each IP address via a single PTR
> record.
>

Sounds great but doesn't that mean I need exactly one unique public IP for
every domain? If I 'skip' the PTR records completely how likely is emails
will be bounced back?

Greetings and thanks
Tobias

> --
> Viktor.
>
>

Re: Ptr DNS and domains

[Viktor Dukhovni]

> On May 9, 2018, at 11:36 AM, Tobias Koeck  wrote:
> 
> if I want to use several domains on my Postfix server do every domain need a 
> unique PTR DNS entry to an unique IP or is it enough to setup $myhostname to 
> the main domain?

1. Though IP addresses can map to multiple PTR records, this is not a good idea.
   Publish exactly one primary name for each IP address via a single PTR record.

2. When handling multiple domains, it is much better to use a single MX hostname
   for them all:

   foo.example. IN MX 0 smtp.example.net.
   bar.example. IN MX 0 smtp.example.net.
   baz.example. IN MX 0 smtp.example.net.
   ...

   Put all the indirection into the MX record, rather than use (outside the SMTP
   standard) CNAMEs in the MX hostname, or define multiple hostnames with the 
same
   underlying IP addresses.

The myhostname setting of a Postfix MTA should ideally be a non-CNAME that maps 
to
its A/ records.

-- 
Viktor.

RE: Ptr DNS and domains

[Fazzina, Angelo]

Hi, I would think if you are relaying mail for multiple domains then you may 
not need to.
I relay/handle mail for many sub domains of uconn.edu and some don’t have PTR 
records.

If it is not a sub domain I think you should follow best practice, and my guess 
is yes you want DNS configured as completely as possible.


-ANGELO FAZZINA

ITS Service Manager:
Spam and Virus Prevention
Mass Mailing
G Suite/Gmail

ang...@uconn.edu
University of Connecticut,  ITS, SSG, Server Systems
860-486-9075

From: owner-postfix-us...@postfix.org  On 
Behalf Of Tobias Koeck
Sent: Wednesday, May 9, 2018 11:36 AM
To: postfix-users@postfix.org
Subject: Ptr DNS and domains

Hi,

if I want to use several domains on my Postfix server do every domain need a 
unique PTR DNS entry to an unique IP or is it enough to setup $myhostname to 
the main domain?

smtp_helo_name = $myhostname
smtpd_proxy_ehlo = $myhostname

Greetings
Tobias