If you have a 3G N7 are you having this issue on wi-fi or just on data? While my Gmail has always worked great on wi-fi or data, I had originally setup my Yahoo on the regular email app for my Bionic. I could not send using data, I could only send using wi-fi. I finally just set Gmail to login and collect my Yahoo and ISP accounts and delete messages from their servers. Gmail identifies which account the message comes from and can even specify which account you want to send from. One stop shopping, all I have to do is check Gmail for all my accounts. My N7 is wi-fi only, but Gmail sends/receives emails just fine.