Exchange Server - still problems with Exchange 2010 and sending to certain domains

We have done the following:

made sure the PTR records matches the IP address of the send connector

created an SPF record

we are still having issues sending to certain domains and we are at a loss.

I have done plenty of 2007 systems and never had this issue.  What are we
doing wrong?

It simply does not make sense.

Do you get an error message back from the receiving server?

JE.