What is Postmark? Transactional email service explained

What is Postmark?

Postmark is an email delivery service for applications, not the ink mark a post office stamps on an envelope. It was announced in October 2009 on the blog of Wildbit, the Philadelphia software company co-founded by Chris and Natalie Nagele, and it has been sending since 2010. ActiveCampaign acquired both Postmark and DMARC Digests from Wildbit in May 2022 on terms that were never disclosed, and the product now trades as ActiveCampaign Postmark.

What makes it structurally different from a general sending service is Message Streams, turned on for every account in October 2020. Transactional and broadcast mail are not merely tagged differently, they run on completely separate servers and IP pools, so a promotional campaign cannot damage the reputation that carries password resets. Opt-out links are required on broadcast streams and not on transactional ones.

The company is unusually willing to refuse business. Every new account is manually reviewed before it may send to anyone outside its own domains, purchased and rented lists are barred by the terms of service, and the support documentation tells senders not to use Postmark to prune a stale list. It also publishes live per-provider delivery speed on a public Time to Inbox page rather than a placement percentage.

The relay and the API are both first-class, with separate hostnames for transactional and broadcast traffic, and sending domains authenticate through a DKIM record plus a return-path CNAME pointing at pm.mtasv.net. A free tier exists but stops at 100 emails a month, so paid use starts at $15 a month for 10,000.