Sending Email Errors

DrJoe, I am having same issue.  Your post and BrianM's reply below has been very helpful.  Here are some more bread crumbs.  The IP address is given to you from your internet service provider. (That is why my phone email is working and my computer is not)  I checked my IP address and it is NOT blacklisted but COX is blocking it for some unknown reason.  I called Tech Support and endured 45 mins of hold then 45 mins of answering silly Tier 1 pre-canned questions by a person who can't spell DNS.  Then I was forwarded to Tier 2.  They were very helpful and elevated my ticket to Tier 3 - who is supposed to remove the COX block on my IP.   

BrianM - it would be extremely helpful if each of the error codes on your site came with additional information on how the user could remedy - in this case an email to Tier 3 would save both Cox and Customer Time.  It would also be helpful to have Cox notify users when they decide to block their IP?  At least then we could get to bottom (or root cause) of why it is being blocked.

WiderMouthOpen - MxToolbox works great!