By default Gmail uses just Http protocol to transfer data. While it may not be an issue if you are just a casual email user, for people whom security is the primary concern, http may not be good enough.
Fortunately, Gmail offers Https, which stands for Hypertext Transfer Protocol Secure, as an option. Https is a standard encryption protocol which is commonly used in online banking services to protect data while in transit.
Forcing Gmail to use Https is easy. On your Gmail, go to Settings and on the General tab, right at the bottom, look for Browser connection. Enable the Always use https option and click Save Changes.
Henceforth, Gmail will always use https to send and receive your mail.