Dropped emails

Xfinity is dropping and bouncing emails from my attorney at suddenlink.net.  Went through all the steps with Xfinitys not-so- helpful technical support and there are no settings in my computer that are causing this.  Tech put me on hold while trying to transfer me to security assurance and disconnected me and did not do a call back, even though he had my phone number.  This happened once before when Comcast was blocking a smaller server a couple of years ago.  I need this fixed and have already spent 2 hours on the phone with customer service and technical support that had been routed to a call center out of the U.S. .  I need help from a technical support employee that is more knowledgeable  here in the States.