Sending mass, customized emails from a Rails app hosted on Heroku

I want to be able to send a monthly email to开发者_如何学Go users of my Rails app hosted on Heroku. However, the email must be customized based on each user's preferences. What's the best way to do this?

Sendgrid does the grunt work. Of sending the emails. It's a paid add on.

Since heroku only allows 30 sec of work per request, you need to use a delayed_job or similar to send out all the emails.

You only need to run the worker on heroku when your job is running.