Thanks for the info, I don't want to rely on google or anyone else, there's always a chance their terms will change, or the service could be withdrawn.
I've decided to handle this another way (my android app is going to talk directly with an epos system and the email part can be handled from there).
I'm having problems getting them to talk to each other over the network, but will post a new question if I can't figure it out.
Thanks for your input, much appreciated.