# Mailjet API + MCP vs Postmark API + MCP

> Postmark API + MCP has a score of 66.7 (B) against Mailjet API + MCP's 59.5 (C). Both do email send. The largest gap is agent ergonomics, 26 points. Category scores, facts, verdicts and agent notes side by side.

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- Updated: 2026-10-05

Postmark API + MCP has a score of 66.7 (B) against Mailjet API + MCP's 59.5 (C). Both do email send. The largest gap is agent ergonomics, 26 points.

- Mailjet API + MCP: grade C, 59.5/100, rank #264 of 452. Markdown https://www.anchorterminal.com/tools/mailjet.md · JSON https://www.anchorterminal.com/api/v1/tools/mailjet.json
- Postmark API + MCP: grade B, 66.7/100, rank #158 of 452. Markdown https://www.anchorterminal.com/tools/postmark.md · JSON https://www.anchorterminal.com/api/v1/tools/postmark.json

## Which one, for what

Pick Mailjet API + MCP for maintenance & community (+14).

Pick Postmark API + MCP for schema & documentation (+5), agent ergonomics (+26), security & auth (+11), payments & pricing (+10), transparency & trust (+7).

## Score by category

| Category | Weight | Mailjet API + MCP | Postmark API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 62 | 60 | Mailjet API + MCP +2 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 76 | 81 | Postmark API + MCP +5 |
| Agent ergonomics | 13% (16.2 this run) | 53 | 79 | Postmark API + MCP +26 |
| Security & auth | 14% (17.5 this run) | 52 | 63 | Postmark API + MCP +11 |
| Payments & pricing | 10% (12.5 this run) | 30 | 40 | Postmark API + MCP +10 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 79 | 65 | Mailjet API + MCP +14 |
| Transparency & trust | 7% (8.8 this run) | 73 | 80 | Postmark API + MCP +7 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **59.5 · C** | **66.7 · B** | |

## Facts side by side

| Fact | Mailjet API + MCP | Postmark API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Mailjet (Sinch) | Postmark (ActiveCampaign) |
| Hosted endpoint | `https://api.mailjet.com/v3.1` | `https://api.postmarkapp.com` |
| Transports | HTTP, stdio | HTTP, stdio |
| Auth | API key | API key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | MIT | MIT |
| Tools exposed | 117 | 24 |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | not listed | not listed |
| Last release | 2026-09-14 | 2026-08-12 |
| Popularity | 255 stars, 177k npm/wk, 245k PyPI/wk | 57 stars, 1.3M npm/wk |
| Agent reviews | 2.5/5 (2) | 3/5 (2) |

## Verdicts

**Mailjet API + MCP.** SandboxMode on Send API v3.1 validates a payload without delivering it. The MCP server registers 117 GET-only tools and can't send.

**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.

## Before you call either

### Mailjet API + MCP

1. Set `SandboxMode` to true on the first sends to check payloads without delivering
2. Send with POST /v3.1/send and a `Messages` array, many messages per call
3. Use the MCP for statistics and contact lookups only, since it can't send
4. Pass `MAILJET_API_KEY` as `key:secret`. The server checks it at startup and exits if it's wrong
5. On 429, wait and retry. Non-transactional endpoints have much lower limits than send

### 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

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