email disappears from inbox

email disappears from inbox.  Others have had this problem.  Some users say only fix is

to delete member completely, then re-add the same member, and the problem goes away.  I can't do that because with the upcoming move to yahoo  a new member can be added BUT WILL HAVE NO EMAIL ADDRESS associated with it (as per comcast document).  So I now have no email for this member.  What now??