Why am I getting errors when sending email with Gmail via SMTP?

Resolution

Gmail have protections in place to avoid their service being used to deliver spam, however these are not published for security reasons. However we often see issues where customer applications attempt to use a Gmail account for email delivery which is subsequently blocked.

To ensure reliable email delivery from apps running on Heroku, we recommend using one of the many email add-ons here: https://elements.heroku.com/addons Many of these have good free plans for low-medium volumes of email as well as excellent analytics and reporting features.