PTR records for IPv6

[SM]

Hi Flavio,
At 19:53 01-09-2013, flavio-cluenet at zipman.it wrote:
>Going back to the topic, when it comes to SMTP (rfc5321) the existance
>of PTR is not strictly required, but, as stated in 4.1.1, in absence of
>reverse mapping the client should use an address literal in the
>helo/ehlo phase instead of an fqdn.

My reading of the text is that if the client cannot determine its 
domain name it can use the address literal instead.  There are 
various techniques which can be used to determine the domain 
name.  The absence of a PTR causes delays.

In terms of operations it's easier if there is a PTR.

Regards,
-sm