Backup To EMail's Configuration window allows you to specify the GMail details. You have to enter your email address. 

In the Merge Split Files tab you can select the path for the files to merge. 

In this window you can fill in many details like the backup to email address and the outgoing server, also the maximum attachment size. 

After pressing Save in the Configuration window, you will have the option to backup to email in the Explorer's context menu.