email woes

I just got an email from a client that I have emailed twice in the last week to keep touch with her and she let me know she hadn't received any of my emails. Nightmare!! I always email people right back and it is my worst nightmare for someone to think I am not emailing them. I stayed up until 2am the night of the Martha show emailing every single person back. akkkk!! So please know I am emailing you and if you are one of my clients and haven't heard from me please email me again. I don't know what is happening, 99.9% of people seem to be getting my emails but I always stress about the one person who might not and then thinks I am being lazy!