Use Postmark when your agent mainly sends: alerts, receipts and sign-in links that must land, with a delivery record you can search for months. It replaces a generic bulk sender for app mail. It is the wrong pick for an agent that holds conversations, because there are no stored threads.
What changed
- · Integration Official MCP server 2.1.1 source
Postmark is a transactional email API run by ActiveCampaign that sends application mail over REST or SMTP, separates transactional from bulk traffic in message streams, parses inbound mail to JSON on its Pro and Platform plans, and ships an official MCP server with 24 annotated tools for agents.
About Postmark
Postmark is a transactional email service now run by ActiveCampaign, which publishes its official MCP server under the ActiveCampaign GitHub organisation. It sends application email such as password resets, receipts and alerts through a REST API or SMTP, and it puts bulk and broadcast mail in separate message streams so a newsletter cannot drag down the reputation of a login code. Every new account starts on a free developer plan that does not expire.
Its edge over newer senders is how much it keeps and how much it explains. Pro and Platform plans store activity and message content for 45 days by default and up to a year, which matters when a support ticket asks why an email from March never arrived. The MCP server includes a diagnoseDelivery tool that checks message history, suppressions and bounces together and answers in plain English, and all of its tools carry read-only, destructive and idempotent hints so a client can gate risky actions.
Postmark fits an agent that mostly sends: alerts, receipts, sign-in links and status updates where deliverability and a long audit trail matter more than holding a conversation. Inbound processing parses incoming mail to JSON and posts it to your webhook, but there is no stored inbox or threading, so a conversational agent belongs on AgentMail or on the Inboxes feature that Resend launched in October 2026. If price per message is the main worry, Amazon SES is cheaper at volume, and SendGrid suits teams already billed through Twilio.
The MCP server runs locally through npx with your server token, which stays on your machine, and works with Claude Desktop, Windsurf and Cursor. Postmark's own MCP page asks readers to confirm they are installing the official server from the ActiveCampaign repository before handing over a token. Our guide to MCP servers explains how to vet a server before you give it a token.
Compare it with the other providers in our email services section, including Cloudflare Email Service for Workers users. Support teams weighing an AI agent on top of their mail should also see our customer support tools guide, and anyone after AI inside a personal inbox will find the email assistants guide a better match than any sending API.
Plans and pricing
Plans read on postmarkapp.com on 6 November 2026, priced by monthly volume of emails sent and received: Free $0 (100 a month, no overage); at 10,000 a month Basic $15, Pro $16.50, Platform $18; at 50,000 Basic $55, Pro $60.50, Platform $66; at 300,000 $245, $269.50 and $294; at 1.5 million $775, $852.50 and $930. Extra emails per 1,000: Basic $1.80, Pro $1.30, Platform $1.20 below 300,000, slightly less above. There is no tier between 100 and 10,000.
Add-ons: dedicated IP $50/mo per IP (Pro or higher, 300,000+ a month), custom activity retention $5/mo (Pro or higher), DMARC monitoring $14/mo per domain. Bootstrapped companies that charge customers can ask support for $75 of credit.
Server plans
| Plan | Price |
|---|---|
| Free (Developer) Cloud · For testing an integration; never expires · Global | $0/mo |
| Basic Cloud · 10,000 emails, 45-day retention, 5 sending domains, no inbound · Global | $15/mo |
| Pro Cloud · 10,000 emails, inbound processing, retention up to 365 days, 10 domains · Global | $16.50/mo |
| Platform Cloud · 10,000 emails, inbound, unlimited sending domains and servers · Global | $18/mo |
Key Features
- Message streams: Transactional and broadcast mail travel in separate streams, up to 30 on Pro, so marketing sends do not share a stream with login codes.
- Inbound processing: On Pro and Platform, incoming mail is parsed to JSON and posted to your webhook, with inbound rules to block senders and an API to search and retry messages.
- Long activity retention: Activity and message content are kept 45 days by default and can be extended to 365 days on Pro and Platform.
- Official MCP server: The MIT-licensed @activecampaign/postmark-mcp package exposes 24 tools across sending, templates, search, diagnostics, bounces, suppressions, webhooks and server info.
- Sandbox mode: A sandbox server accepts API calls and can generate fake bounces without delivering anything, useful for testing an agent's error handling.
Strengths
- Separating transactional and bulk traffic by stream protects the deliverability of the messages users are waiting for.
- Up to a year of searchable activity on Pro and Platform outlasts the month Resend keeps and the week SendGrid Pro keeps by default.
- Its MCP tools are annotated as read-only or destructive, which lets an agent client ask before deleting a template or suppression.
Weaknesses
- No stored inbox or threading: inbound mail arrives as a webhook payload, and keeping the conversation is your job.
- The free plan is 100 emails a month with no inbound, and the next step up is a 10,000-email tier, so there is no small paid plan.
- Received mail counts toward billed volume, and inbound needs Pro or Platform rather than Basic.
Frequently Asked Questions
What does Postmark actually cost?
At 10,000 emails a month, Basic is $15, Pro $16.50 and Platform $18, and at 50,000 the same three cost $55, $60.50 and $66, according to Postmark's pricing page on 6 November 2026. Overage runs $1.80, $1.30 and $1.20 per 1,000 respectively. Volume includes the mail you receive, so a reply-heavy agent pays for both directions.
Can you use Postmark without paying?
Yes, every account starts on a free developer plan of 100 emails a month that never expires, but it allows no overage and has no inbound processing. That is enough to test an integration, not to run an agent. The next step is a 10,000-email paid tier, because Postmark sells nothing in between.
What are Postmark's closest competitors?
SendGrid is the volume incumbent and adds marketing campaigns, but its free option is a 60-day trial. Amazon SES costs far less per message and leaves the dashboard and diagnostics to you. For agents that must read and answer mail, AgentMail and Resend's Inboxes store threads, which Postmark does not.
How does Postmark compare to SendGrid in 2026?
Postmark keeps a permanent free plan and lets Pro and Platform customers keep activity for up to a year, while SendGrid's Essentials plan keeps 3 days of email activity and Pro keeps 7 unless you buy more. SendGrid is the better fit for high-volume marketing and teams already on Twilio. For transactional mail an agent sends, Postmark is the more careful choice.
How do you set up Postmark?
Create an account, add a sender signature or verify a domain with DKIM and Return-Path records, and send through the API or SMTP with your server token. To receive mail, upgrade to Pro, create an inbound server and point it at your webhook URL. For agent access, run npx -y @activecampaign/postmark-mcp with POSTMARK_SERVER_TOKEN set.
Top Alternatives
- SendGrid: Pick Postmark for a permanent free plan and up to a year of activity; pick SendGrid for marketing campaigns and Twilio billing.
- Resend: Pick Postmark for send-only mail with long retention; pick Resend when an agent must reply inside stored threads.
- Amazon SES: Pick Postmark for a dashboard and diagnostics out of the box; pick Amazon SES when cost per message rules.
- AgentMail: Pick Postmark for one-way app mail; pick AgentMail when each agent needs an inbox it can read.
Hokai guides that mention Postmark
- Best Email APIs for AI Agents in 2026: Inbox or Webhook?: Six email APIs for AI agents compared: which give an agent a real inbox, what 10,000 emails each way cost, free-plan catches, retention and safety controls.