Reverse Dns Question...is it really necessary or not?

[Len Conrad]

> >They may indeed have address->name mappings, but very seldom does
> >one have an MX record. Not MX record, then it is not a legitimate
> >mail relay.

This is a total BS conclusion.

The following is all you need, and it is my recommended best practice:

A _single_ PTR record per the (outbound) MTA's IP:

d.c.b.a.in-addr.arpa. PTR  mx1.domain.tld.

and a single A record for its PTR hostname:

mx1.domain.tld. A a.b.c.d

... period. The above records have no relationship with or dependence upon:

1. any MX records, nor any

2. any envelope sender/recipient domains that transit the IP.

The above are DNS settings are referred to as "matching" PTR and A records.


Going a little further, I also recommend that two SMTP values should match 
the above hostname, if only because "why not?", and to encourage people 
learn what their ofen-ignored below are:

the SMTP-greeting hostname:

220 mx1.domain.tld

and the HELO hostname:

EHLO mx1.domain.tld


With the above 2 DNS records and the 2 SMTP/MTA settings, you'll have no 
difficulty getting your mail delivered to MTAs that use DNS/SMTP values as 
validations or credentials for the sending IP.   Many, and probaly 
increasingly more, MX either insist on PTR/A matching, or, will weight the 
absence of PTR/A matching as heavily as no PTR.  My own policies consider 
no PTR to be one foot in hell, and one more "envelope stage" error will 
cause rejection after RCPT TO:

And the 4 settings above will even get your mail past extreme checks, quite 
rare, that insist the SMTP greeting/helo hostnames MUST match the PTR/A 
records.

Further SMTP settings are accounts for the above hostname:

abuse at mx1.domain.tld

postmaster at mx1.domain.tld

and for the domain literals:

postmaster@[a.b.c.d]
abuse@[a.b.c.d]

The anonymous postmaster@ and abuse@ accounts should end up in a person's 
mailbox.


Len


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