I just set up an Ubuntu 14.04 server on Digital Ocean. One "apt-get install mail-stack-delivery", and one edited line in /etc/postfix/master.cf later (just to get 587 submission working) and I have my own mail server including STARTTLS on smtp and imap. Made me wonder, will we see sync options on Ubuntu Phone to sync mail/calendar/own-cloud with one (SSH) account? Seems to me the possibilities are endless and very exciting. Please stay true to FOSS principles, resist the temptations, give the (mobile) web back to the people!
Certainly you can encrypt the email part, But I'm not sure how NSA proof it will be when the whole server is in the RAM of one that you don't control though.