It can be stressful when emails suddenly go "missing" from your mailbox. When this happens, it's usually due to another program or app the account is being accessed from. It may be set up to download emails from our server but not leave a copy of them when it does, making it look like emails disappeared. What's more, syncing issues between the account and a non-Yahoo mail app can cause emails to be removed from our servers and be deleted or moved to the app instead. If you currently access the account through an app, or have in the past, you may want to remove the account there and re-add it to resolve any syncing issues in the future.
If needed, you can request a Mail restore here. We can attempt to restore emails that have been removed in the past 7 days, except those from the Drafts or Spam folders. If emails were deleted from the Sent folder directly, then they may be able to be restored right back to that folder. However, if they were deleted (put into Trash) and then restored, they may be in the Trash folder and can’t be moved back to the Sent folder. Keep in mind though that restores aren't guaranteed and that most emails are restored to the Trash folder.
Sometimes, emails may not actually be missing from the account but are just tucked away or hard to find. In these cases, try doing a Search for the email in your mailbox or disabling Conversations to make things easier to see. If you're looking for a specific photo or attachment, you can use the Photos or Documents Views in New Mail, respectively.