Mandrill offers a paid monthly plan.
Users on a paid monthly plan can choose the number of emails that they expect to send in "blocks" of 25,000. We built discounts into our payment structure, so your per-email pricing automatically decreases as you send more email. Calculate your monthly costs and view example volumes on our pricing page.
Mandrill counts each recipient as one email for credits and billing. For example, if you send one SMTP message to five recipients or include five recipients in your API request, we'll count that as five email credits toward your monthly limit.