I would tend to disagree that building upon another platform like Gmail is "strategically hampered". We (streak.com) think its the only way to get users to swit

I would tend to disagree that building upon another platform like Gmail is "strategically hampered". We (streak.com) think its the only way to get users to switch to your email service - build it on top of their existing email client (gmail) and slowly start replacing pieces of the Gmail stack until they are exclusively using you. Thats been our not-so-secret strategy from the beginning. It allows the user to slowly onboard to your product instead of making a one time "do I want to switch over my email?" type of decision which is obviously much harder.