I do it by using a PHP script on one of my servers, the SIM800 connects to the PHP script, which uploads the readings to a MYSQL database, and also emails the data to a number of different addresses (the addresses of which are stored in another MYSQL table). I never even looked into sending emails directly, as I need to write to the MYSQL database anyway, and doing it all via PHP scripts allows you to make most changes server side, rather than in the SIM800 programming.