If you use a computer and an application to read the email, then those emails have been stored into one big database usually in .dat format. My advice is to use a recovery solution (Recuva) to scan for the file. Install the application, set the path where the application is installed and chose other as file type to exclude music, pictures, videos, etc. Once you locate the files restore it to its initial location.
Additionally, there is also the possibility for the emails to be lost forever and the only way to get recover information is by contacting Verizon.