Yes. The reason is that sending transactional emails is not free.

Your plan includes sending transactional emails (newsletter to your members) for the first 1000 emails sent/month. If you need to send more emails, we will charge you 5$/month for every 2500 emails sent/month.

You might be aware that we use Mailgun to do so. See also: How is it interconnected? (FirePress, Ghost, Mailgun, Membership, Stripe, Payments)

You've successfully subscribed to FirePress
Welcome back! You've successfully signed in.
Great! You've successfully signed up.
Success! Your account is fully activated, you now have access to all content.