rDNS/DNS problem

[Bill.Light at kp.org]

I thought I had this squared away, but I'm getting a bounce message from 
craigslist.com saying my "DNS/DNS validation failed."
The specifics:

mail.light-family.com at 66.124.156.123,  handles mail for itself  as well 
as a few (family) virtual domains.
One of the domains:   hall-brothers.com, used by my son 
sons-name at hall-brothers.com sent the e-mail...and received the bounce.

Can someone on the "outside" tell what I have done wrong please?

Bill