Reverse lookup of selected IP addresses without delegation agreement?

[Ralph]

Len Conrad wrote:

 > MTAs like postfix will consider a PTR hostname to be invalid if the
 > PTR hostname doesn't have matching A record

Yep. Among other things, it is Postfix I am trying to appease here,
and I don't want to use check_client_access with a CIDR lookup table
in this special scenario.

I thought that returning mail.sourceforge.net was the right thing to
do because the the A record is available:

   $ dig mail.sourceforge.net
   mail.sourceforge.net. 6417 IN A 66.35.250.206

As dig'ing lists.sourceforge.net returns the same, it probably does
not matter too much... Anyway, I think I am beginning to got the hang
of things. Thanks, Len!

Ralph