You may suddenly discover that you are not receiving emails in your inbox. However if you look in the trash box you will discover them there. You can move them from the trash box to the inbox.
This can occur from having spyware or viruses on your machine or your email account being hacked.
The very first thing I would suggest doing is change the password for your email account. In Yahoo email accounts (includes BellSouth, ATT, etc) you will click in the upper right corner on where it says Hi and your name and choose Account Info and it will ask for your password. Then it will give several options including changing your password. There will be a similar approach in other email systems to find your account information.
Secondly you want to clear filters in your email. Filters are used to put certain email in different boxes automatically to make managing it easier. Most people never use filters. In this case the virus or hacker has set a filter in your email that sends all email to the trash. In Yahoo email you will click the sprocket looking wheel in the upper right corner and then choose mail options on the list that appears beneath it. Then another page will appear and on it you can choose Filters on the list on the left near the bottom of the list. Then assuming you use no filters choose all that are listed and then click the trash can icon at the top to remove them.
In Microsoft email systems (outlook.com, hotmail.com, live.com) you will click on the sprocket wheel in the upper right corner to do all these steps; password change and filters are both contained there.