Send automated messages based on certain criteria

We've been testing out granting a rank to users who have logged in twice but not posted yet as a way to send those people an email encouraging them to make their first post in the community. We've gone from 13% to 20% of people who have made at least one post so this is great!

I'd love to be able to send more messages targeted in this way, but without having to set up a rank for all of them.