Ptr DNS and domains

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Ptr DNS and domains

Tobias Koeck
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

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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

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G Suite/Gmail

 

[hidden email]

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From: [hidden email] <[hidden email]> On Behalf Of Tobias Koeck
Sent: Wednesday, May 9, 2018 11:36 AM
To: [hidden email]
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

 

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Re: Ptr DNS and domains

Viktor Dukhovni
In reply to this post by Tobias Koeck


> On May 9, 2018, at 11:36 AM, Tobias Koeck <[hidden email]> 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/AAAA records.

--
        Viktor.

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Re: Ptr DNS and domains

Tobias Koeck


On Wed, May 9, 2018 at 5:59 PM, Viktor Dukhovni <[hidden email]> 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.


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Re: Ptr DNS and domains

Viktor Dukhovni


> On May 9, 2018, at 12:11 PM, Tobias Koeck <[hidden email]> 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.