I am trying to send emails from Heroku up and running. At the moment I can send emails from Heroku via the \"tutorial\" at http://blog.heroku.com/archives/2009/11/9/tech_sen
I have personally encountered that error sending with Gmail and needed to solve an unlock CAPTCHA to allow the sending. Gmail can be picky with security sometimes, and the documentation is not very apparent.
The full message should read:
530-5.5.1 Authentication Required. Learn more at https://support.google.com/mail/bin/answer.py?hl=en&answer=14257
so check out that link and follow the directions there.
You might need to sign into the Gmail webapp or (what I had to do), solve the unlock CAPTCHA. Or perhaps it is something in your app or environment, but following the Google directions is worth a shot.