Excellent questions. It is free unless you want to use custom fields. The emails go into a queue which is listened for and processed when items are added. I have 3 that listeners that run simultaneously to handle email sending.
If the site goes down then the emails are lost. I'm still working on a solution of multi region load balancing with high availability to ensure this doesn't happen.
If the site goes down then the emails are lost. I'm still working on a solution of multi region load balancing with high availability to ensure this doesn't happen.