Nightngale.......people email me all the time messages that I never see, and when I finally talk to them by phone, they want to know why I am not responding to their email messages.
The reason why is because the only email messages that I receive in my inbox are from those whose email addresses are listed in my email address book and/or on my "safe list" of emails to put in my box.
All other emails who have addresses that are not listed on those two items mentioned, are automatically deleted without my having known they were sent to me.
I have my email preferences set to only receive email from addresses listed in my email addy and/or on my email "safe list".
I also have my email settings to automatically delete unrecognized email addresses immediately......instead of on a delayed deletion setting.
Do you know how your email account is set up? What email options have you chosen for your account? If you share your computer with anyone else, check and see what email settings you may be sharing with them.