Pepipost is built on the philosophy to encourage good senders and to keep the email eco-system clean.
85% of today's email is Spam and Pepipost don't want to add up to that.
They built their pricing model so they don't charge for the emails which are being opened by the customers. Emails that are clicked, opened or engaged with are free.
Industry stats says 35-40% is the average open rate, hence that much of email volumes can be free. There is no limits, More your customer engagement is lesser will be your marketing spends at Pepipost.