Here are some tips to help you figure out what may be happening to your emails.
The first place to check is your spam/junk folder. If you find the email(s) - great! If this happens consistently you can try the following: click on one of the messages and then More, Filter emails like this, leave the address as is and other fields blank and create the filter to have these emails to go to your inbox.
If they aren't there, please confirm the email was actually sent to you by the system. In Your Profile you will see a blue link that tells you how many emails have been sent to you at the email address associated with Your Profile.
Click on that link to see all the emails. You can see if the email bounced as well as when it was first opened and last opened. Let us know at email@example.com and include all of the available information about the email(s) you did not receive (sent date, to email, email type, subject). This way we can pinpoint the source of the problem.
Note: If you are a site/org administrator, you can go to People tab and click on the person(s) name to see their Sent list.
Here is a help video that may help. It is specifically for Yahoo email users.