please dont be offended. But i deal with a lot of people here and sometimes silly things slip through so i have to start with the most likely simple cause
please click on the actual word date or received above the column that says when an email was received. This will sort the emails by date and you may find that you have them all they just werent sorted correctly.
click again if they are in the wrong order and they will toggle from newest to oldest to oldest to newest etc. and make sure that you scroll to the top or bottom after you have sorted them this way.
if that does not work i have other options including reversing the upgrade by using a system restore. and or making sure that you have loaded the correct data file. or have it selected in the left hand section where it shows the folders.
I can also log in remotely to fix it for you if you want to spend a little more money.
System restore instructions - windows 7 8 10
hold the windows logo key and hit R
in the box that appears type
select restore to an earlier date.
Under the "suggested restore" which is usually not old enough to help is a link for "OTHER RESTORE POINTS"
click that if the suggested ones are not BEFORE THE PROBLEM STARTED
choose a date from the calendar that is BEFORE you experienced the problem
hit ok / restore
the computer will start to shut down
a restoring settings box will appear with a status bar
when it finishes your computer will restart with the same settings it had on the date you restored to. your data will not be affected.
It is not perfect. But it fixes a lot of things.