My previous setup to send from multiple email addresses works well in iOS 6. Recently, I have to reconfigure my Gmail account and the previous setup doesn’t work any more. Mail cannot connect to Gmail and I would be prompted with the following message: Cannot get Gmail: The user name or password for imap.gmail.com is incorrect.
Modern Nerd shares how you can send from multiple email addresses from your iPhone or iPad, under your Gmail account. Works well for my iPhone, on iOS 6. Check out the link here, Multiple “From” Email Address on iPhone and iPad