Mail PTR Records

[Matt Kettler]

What does this have to do with the topic of discussion?

We're not talking about validation of HELO/EHLO parameters. We're talking about 
verifying that the IP the connection originates from has a PTR record.

The below portion of 2821 is irrelevant here, as it pertains to the parameter to 
HELO/EHLO only.

Nathan Olson wrote:
> RFC 2821
> 
> 4.1.4 Order of Commands
> 
> The SMTP client MUST, if possible, ensure that the domain parameter
> to the EHLO command is a valid principal host name (not a CNAME or MX
> name) for its host.  If this is not possible (e.g., when the client's
> address is dynamically assigned and the client does not have an
> obvious name), an address literal SHOULD be substituted for the
> domain name and supplemental information provided that will assist in
> identifying the client.
> 
> An SMTP server MAY verify that the domain name parameter in the EHLO
> command actually corresponds to the IP address of the client.
> However, the server MUST NOT refuse to accept a message for this
> reason if the verification fails: the information about verification
> failure is for logging and tracing only.