A belated thank you to TCH-Alex - responding to my May 2016 post.
Bernice, I'm not an expert - so maybe someone else will chime in, but here are some ideas to help prevent such events (lost deleted email) in the future.
Consider using POP3 mail and setting your email client to "never delete" from server (or maybe delete after 6 months - or a year, etc).
Get into the habit of archiving more.
As far as "so what to do, if this won't help?"
Regular backups (you should already be doing this) may enable you to retrieve deleted email (though it may be a pain to find the appropriate files and then view them).
This has been my strategy, to generously save (archive) mail in about 40 different folders set up in my email client (Thunderbird) and backup daily; automatically to the cloud.