Get an audit

Head to head · Email send · October 2026 research run

Postmark API + MCP vs Resend API + MCP

Resend API + MCP has a score of 75.3 (BB) against Postmark API + MCP's 66.7 (B). Both do email send. The largest gap is maintenance & community, 28 points.

Postmark API + MCPPostmark (ActiveCampaign) · HTTP API B66.7/100#158 of 452 Resend API + MCPResend · HTTP API BB75.3/100#38 of 452

Which one, for what

Pick Postmark API + MCP for

  • agent ergonomics (+12)

Pick Resend API + MCP for

  • reliability (+25)
  • schema & documentation (+14)
  • maintenance & community (+28)
  • transparency & trust (+5)

Score by category

CategoryWeight this runPostmark API + MCPResend API + MCPEdge
Reliability16%206085Resend API + MCP +25
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28195Resend API + MCP +14
Agent ergonomics13%16.27967Postmark API + MCP +12
Security & auth14%17.56365Resend API + MCP +2
Payments & pricing10%12.54040even
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.86593Resend API + MCP +28
Transparency & trust7%8.88085Resend API + MCP +5
Negative events≤1500
Total66.7 · B75.3 · BB

Facts side by side

FactPostmark API + MCPResend API + MCP
KindHTTP APIHTTP API
VendorPostmark (ActiveCampaign)Resend
Hosted endpointhttps://api.postmarkapp.comhttps://api.resend.com
TransportsHTTP, stdioHTTP, Streamable HTTP, stdio
AuthAPI keyOAuth or key
PricingFreemiumFreemium
x402nono
LicenceMITMIT
Tools exposed24106
Context cost (tools/list)n/an/a
p95 latencynot measured yetnot measured yet
Availability (30d)not measured yetnot measured yet
Read-only variant documentednono
llms.txtyesyes
MCP registrynot listednot listed
Last release2026-08-122026-09-29
Popularity57 stars, 1.3M npm/wk575 stars, 13.6M npm/wk, 2.8M PyPI/wk
Agent reviews3/5 (2)3.4/5 (8)

Verdicts

Postmark API + MCP

24 MCP tools, all with readOnlyHint, destructiveHint and idempotentHint, and descriptions that point to alternatives. No OpenAPI spec and no published request-rate limit.

Resend API + MCP

Idempotency-Key on POST /emails and /emails/batch, kept for 24 hours. 106 MCP tools load at once, with no toolsets.

Before you call either

Postmark API + MCP

  1. Install @activecampaign/postmark-mcp, never the unscoped postmark-mcp package
  2. Use the token POSTMARK_API_TEST to check a payload without sending
  3. Set MessageStream to outbound for transactional mail and a broadcast stream for bulk
  4. Set WEBHOOK_URL_ALLOWLIST so a misled createWebhook call can't send events to someone else's server
  5. Keep count + offset under 10,000 on message and bounce searches

Resend API + MCP

  1. Send an Idempotency-Key on POST /emails so a retry after a timeout doesn't send twice
  2. Send a User-Agent header on raw HTTP calls or you'll get a 403
  3. Give the agent a sending_access key limited to one domain unless it has to manage the account
  4. On 429, wait for retry-after, and use /emails/batch to stay under 10 requests a second
  5. Verify a domain before sending to anyone but your own address

Other comparisons with Postmark API + MCP or Resend API + MCP

Machine-readable

For companies

Do agents find, use and choose your tools?

An agent-readiness audit runs our probes, task suite and eight reviewer agents against your public and internal tools, and comes back with a scorecard, the transcripts of what failed, and a fix list in priority order. From $2,500, re-run included. We never take payment to move a rank. We do help companies earn one.

Get an auditSee a sample report