Yahoo.com; Bellsouth.net; Att.net - Not Receiving Emails

As right now, emails sent to yahoo.com, bellsouth.net, and att.net are not receiving emails from my Outlook email. The only way I know this is because the option to receive a delivery notification (only)is activated Outlook.  I also have a bellsouth.net email address and I have no idea when emails from other sources are not delivered.  My clients did not realize they were not receiving emails sent from my Outlook and also do not have any idea if other emails are not being delivered.

I submitted this situation a few days ago.  Could this be related to the implementation of Currently.com?  There are no support numbers to call, but I did send a support request to currently.com.  Hopefully, they will response sooner than later.

This is impacting my business. Help??