>you pay once for it to be received by mailgun servers, and once for it to be delivered to your webhook.
Mailgunner here. This does not sound right. Can you please reach out to me via address in profile? Mailgun does not charge for webhooks, you're probably confsuing this with email relaying (which we also do).
Also it is impossible to have complimentary inbound email of production quality due to the need for quality spam filtering. Handling spam in production setting (throughput, quality of service, uptime, performance) for free would mean wiping out CloudMark and other spam filtering vendors.
In other words, as always, you get what you pay for. Mailgun has always been known for being a true bi-directional programmable ESP and a sizable percentage of our traffic is inbound.
SendGrid and Mandrill inbound is currently complimentary to customers.
To receive an inbound email via Mailgun, you pay once for it to be received by mailgun servers, and once for it to be delivered to your webhook.