Are there any limits on transactional emails ?
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)