Gmail offers a search feature similar to Google search. It is very easy to use.
If you are looking for emails that are in your trash folder or in your archive folder or inside you spam folder, use the following method to search.
So if you are search for emails from David and you do not know where it is, type in:anywhere from:David
This Gmail search will bring the emails from all the folders including Gmail spam folder and Gmail trash folder.
You can do advanced search along with this search, like search subject or exact words or email sent to.
If you have any questions or suggestions, post a comment.