First off, I apologize for the list. I didn't realize my replies included the entire original email...
Mark, we do not run a mail server. The issue is a lot of our customers have their 2nd homes here,
so when they come up they are using their email provided by their 1st home ISP.
A number of our customers use Cox, Charter, and Spectrum and can receive email just fine but cannot send.
Report from a mac book pro email client showed Cox to be blocking the IP that we NAT most customers through.