Since June 2009 Google has been testing the https protocol in order to use it in the whole Gmail service so us to provide the optimum security possible from the information send/received from/to the browser of the user to/from the company’s servers. Through these months Google upgraded only the login page of Gmail to encrypt the username and password of the user also offering the option to the user to enable https if he/she wanted to. On the 12th of January Google announced through the official Gmail Blog that https will be the default option from now on for all the users, and only if the user wishes so, he or she can go back to the unsecure https protocol.
Several issues were resolved by Google until now, concerning the use of https to its services, there is still though an issue for the users who use the offline Gmail. More information about the issue can be found here.