I have been trying to find an iOS app which will let me send email from various accounts without going through Mail.app.
I know about the comma trick but that is not what I am after.
I also do not want to setup multiple accounts in Mail.app (which is going to give me multiple Inboxes, even if they are empty).
The closest solution I have found is Ginbox but unfortunately it seems to be broken under recent versions of iOS, and even if it worked, it's not a great solution, since it requires loading each Gmail account separately when you want to send an email from a different account.)
(If it doesn't exist… free iOS app idea!)