Are there any other iOS apps other than Mail which can send email? 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!)
The iOS version of Sparrow has just been released, and it contains this functionality. In the settings for email accounts you can set up aliases. You can also set up a custom signature and SMTP server for each alias:




When composing a message, by default it will be sent from your default alias. If you want to change this, tap the "From" in the top center and you will be able to select which alias you want this message to come from:


 

Sparrow is available in the App Store.