Incoming email periodically disappears. This has happened to me for a fact several times. I read an email and then it is gone. I never deleted it, when I search for it across all my folders it is nowhere to be found. This is obviously a bug that needs to get fixed and I don't see a way to report bugs like this. A related problem is when I ask for the missing email to be restored, the only options are that either I deleted it, or my account was hacked. In this case, obviously it was neither. So here are my suggestions:
1. Create a way for users to submit bugs, not just just improvement suggestions.
2. In the help request for restoring emails, there should be another options beyond just that the email was accidentally deleted or the account was hacked. It can be a Yahoo bug for example.