This is almost exactly what I was going to write. Don't be afraid to send episode alerts if people clicked a button labelled "episode alerts" and signed up for

This is almost exactly what I was going to write. Don't be afraid to send episode alerts if people clicked a button labelled "episode alerts" and signed up for a mailing list caled "episode alerts". But if you see a value in less-frequent, make that an option. Or try to actually track it to see which is working. If you send every 3 episodes, do people watch all three? When you send a mail, do you see more eyeballs on the first, or more eyeballs on the more recent? I guess the risk here is that you're getting 33% of the engagement to save 1% churn. Is 1\1000 worth more than 3\990?