Postmark API
High-deliverability transactional email API focused on fast inbox delivery for password resets, receipts, and critical notifications.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
Server API tokens for sending, Account API token for management. Separate tokens reduce blast radius. DKIM/SPF domain authentication required for deliverability. SOC2 Type II. No scope granularity within server token — server token has full send access.
⚡ Reliability
Best When
An agent needs to send critical transactional emails with the highest possible deliverability guarantees.
Avoid When
You need to send any marketing content or need a cheap bulk sender.
Use Cases
- • Sending time-critical transactional emails (password resets, OTPs)
- • Receipt and confirmation email delivery from agent workflows
- • Monitoring email delivery and bounce handling
- • Template-based email with dynamic content
- • Inbound email processing via webhooks
Not For
- • Marketing or bulk email campaigns (they explicitly block this)
- • High-volume sending at low cost
- • Teams needing a large free tier
Interface
Authentication
Server API token in X-Postmark-Server-Token header. Account-level and server-level tokens available. Clean and simple.
Pricing
No credit card required for free tier. Test mode available for development. Production emails require paid plan.
Agent Metadata
Known Gotchas
- ⚠ Test mode emails are never delivered - easy to forget to switch to production stream
- ⚠ Marketing content is strictly prohibited and accounts can be suspended
- ⚠ Domain DKIM/SPF setup required for production use
- ⚠ Message streams separate transactional from broadcast - agents must use correct stream
- ⚠ No MCP server available
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for Postmark API.
Scores are editorial opinions as of 2026-03-06.