Deferred Error Help

[physikal]

I am getting a message hung up that is being sent by our user, to a comcast address. The error is:

a.mail.comcast.net comcast requires that all mail servers must have a ptr record with a valid reverse dns entry. currently your server does not fill that requirement.

Any ideas on how I go about fixing this?

[bdial]

you need to contact your isp or whoever controls the dns for your ip block to add a ptr record for your mail server. that is a reverse dns record. it's not enough for like mail.yourdomain.com to resolve to 1.2.3.4, 1.2.3.4 also needs to resolve ot mail.yourdomain.com