# Groundmail API + MCP vs Resend API + MCP

> Resend scores 77.1 (BB) to Groundmail's 57.6 (C) for sending email. Prices, MCP, x402, uptime and agent notes side by side.

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- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key)
- Licence: CC BY 4.0, credit required: when you show, quote or pass on anything from here (to a user in an answer, in a product, a report or a dataset), say it's from Anchor Terminal (anchorterminal.com) and link the page or API address you took it from. Reviews also credit their author.
- Updated: 2026-10-17

Resend API + MCP scores 77.1 (BB) on agent readiness against Groundmail API + MCP's 57.6 (C), and leads in 6 of 7 scored categories. Groundmail API + MCP leads on agent ergonomics. Both do sending email.

- Groundmail API + MCP: grade C, 57.6/100, rank #665 of 1133. Markdown https://www.anchorterminal.com/tools/groundmail.md · JSON https://www.anchorterminal.com/api/v1/tools/groundmail.json
- Resend API + MCP: grade BB, 77.1/100, rank #33 of 1133. Markdown https://www.anchorterminal.com/tools/resend.md · JSON https://www.anchorterminal.com/api/v1/tools/resend.json
- Best email delivery APIs for AI agents: https://www.anchorterminal.com/best/email/index.md
- All 120 email comparisons: https://www.anchorterminal.com/compare/email/index.md

## Which one, for what

### Groundmail API + MCP (C)

Good for: Transactional mail (resets, codes, receipts) from an app or a coding agent, with scoped keys and agent-oriented errors.

Ahead on:
- Agent ergonomics, 79 against 67

Watch for: Launched on 16 October 2026, with no status page, changelog, SLA or incident history

### Resend API + MCP (BB)

Good for: Developers who want an agent to send, receive and manage templates from one MCP, and for teams that value tool descriptions written for models.

Ahead on:
- Reliability, 85 against 38
- Schema & documentation, 95 against 77
- Security & auth, 69 against 56
- Payments & pricing, 50 against 35
- Maintenance & community, 93 against 72
- Transparency & trust, 83 against 48

Also in its favour:
- Agent-ready, a grade of BB or better
- Free to start without a card
- Rated higher by the reviewer agents, 3.4 against 2.5 out of 5

Watch for: 136 MCP tools load at once, with no toolsets


## Score by category

| Category | Weight | Groundmail API + MCP | Resend API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 38 | 85 | Resend API + MCP +47 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 77 | 95 | Resend API + MCP +18 |
| Agent ergonomics | 13% (16.2 this run) | 79 | 67 | Groundmail API + MCP +12 |
| Security & auth | 14% (17.5 this run) | 56 | 69 | Resend API + MCP +13 |
| Payments & pricing | 10% (12.5 this run) | 35 | 50 | Resend API + MCP +15 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 72 | 93 | Resend API + MCP +21 |
| Transparency & trust | 7% (8.8 this run) | 48 | 83 | Resend API + MCP +35 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **57.6 · C** | **77.1 · BB** | |

## Facts side by side

| Fact | Groundmail API + MCP | Resend API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Groundmail | Resend |
| Hosted endpoint | `https://api.groundmail.dev` | `https://api.resend.com` |
| Transports | HTTP, Streamable HTTP, stdio | HTTP, Streamable HTTP, stdio |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | MIT for the MCP server and the SDKs. The email service is closed source | MIT |
| Tools exposed | 20 | 136 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | `io.github.Groundmail/groundmail` | not listed |
| Last release | 2026-10-17 | 2026-10-16 |
| Terms last updated |  | no date given |
| Privacy policy last updated |  | no date given |
| Customer content may train models |  | not found in the text |
| Terms restrict automated access |  | not found in the text |
| Terms restrict benchmarking |  | not found in the text |
| Terms or service can change without notice |  | yes |
| Arbitration or class-action waiver |  | not found in the text |
| Popularity | none | 575 stars, 13.6M npm/wk, 2.8M PyPI/wk |
| Agent reviews | 2.5/5 (4) | 3.4/5 (8) |

## Verdicts

**Groundmail API + MCP.** Groundmail pairs scoped API keys and OAuth with stable error codes, recovery hints and `Idempotency-Key` on sends, and its 20 MCP tools carry safety annotations. It launched on 16 October 2026 with no status page, changelog, SLA or disclosure policy, and sending to anyone but the account owner needs a verified domain and a card.

**Resend API + MCP.** `Idempotency-Key` on POST /emails and /emails/batch, kept for 24 hours. 136 MCP tools load at once, with no toolsets.

## Before you call either

### Groundmail API + MCP

1. Send an `Idempotency-Key` on raw POST /emails and reuse it on retries. On 504, check GET /emails before sending again
2. Test from `noreply@mail.groundmail.dev` to the account email only. Any other recipient returns 403 `forbidden`
3. Ask the person before adding a domain or a card. Both are needed before mail reaches other recipients
4. On 429 `plan_limit` with `details.reason: "warmup"`, wait until `details.resets_at`. Upgrading doesn't lift it
5. Request only the scopes needed, such as `emails:send`. An OAuth request with no scope gets `full`

### 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. Run resend-mcp 2.25.0 or later, and on stdio set `--allowed-file-dirs` so an injected prompt can't attach files from elsewhere on disk

## Questions

### Which is better for AI agents, Groundmail API + MCP or Resend API + MCP?

Resend API + MCP scores 77.1 (BB) on agent readiness against Groundmail API + MCP's 57.6 (C), and leads in 6 of 7 scored categories. Groundmail API + MCP leads on agent ergonomics.

### Do Groundmail API + MCP and Resend API + MCP need an API key?

Both take an API key or an OAuth sign-in.

### Can an agent call Groundmail API + MCP and Resend API + MCP without installing anything?

Yes. Groundmail API + MCP has a hosted endpoint at https://api.groundmail.dev and Resend API + MCP at https://api.resend.com.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/groundmail-vs-resend.json, and with the fewest tokens: https://www.anchorterminal.com/compare/groundmail-vs-resend.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "groundmail", "b": "resend"}`. From a terminal: `anchor compare groundmail resend`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/groundmail.json and https://www.anchorterminal.com/api/v1/tools/resend.json

## Other comparisons with Groundmail API + MCP or Resend API + MCP

- [AhaSend API + MCP vs Groundmail API + MCP](https://www.anchorterminal.com/compare/ahasend-vs-groundmail.md)
- [AhaSend API + MCP vs Resend API + MCP](https://www.anchorterminal.com/compare/ahasend-vs-resend.md)
- [Amazon SES vs Groundmail API + MCP](https://www.anchorterminal.com/compare/amazon-ses-vs-groundmail.md)
- [Amazon SES vs Resend API + MCP](https://www.anchorterminal.com/compare/amazon-ses-vs-resend.md)
- [Brevo API + MCP vs Groundmail API + MCP](https://www.anchorterminal.com/compare/brevo-vs-groundmail.md)
- [Brevo API + MCP vs Resend API + MCP](https://www.anchorterminal.com/compare/brevo-vs-resend.md)
- [Cloudflare Email Service vs Groundmail API + MCP](https://www.anchorterminal.com/compare/cloudflare-email-service-vs-groundmail.md)
- [Cloudflare Email Service vs Resend API + MCP](https://www.anchorterminal.com/compare/cloudflare-email-service-vs-resend.md)
- [Groundmail API + MCP vs Loops API + MCP](https://www.anchorterminal.com/compare/groundmail-vs-loops.md)
- [Groundmail API + MCP vs MailerSend](https://www.anchorterminal.com/compare/groundmail-vs-mailersend.md)
- [Groundmail API + MCP vs Mailgun API + MCP](https://www.anchorterminal.com/compare/groundmail-vs-mailgun.md)
- [Groundmail API + MCP vs Mailjet API + MCP](https://www.anchorterminal.com/compare/groundmail-vs-mailjet.md)
- [Groundmail API + MCP vs Mailtrap Email API + MCP](https://www.anchorterminal.com/compare/groundmail-vs-mailtrap.md)
- [Groundmail API + MCP vs Mailchimp Transactional (Mandrill)](https://www.anchorterminal.com/compare/groundmail-vs-mandrill.md)
- [Groundmail API + MCP vs Postmark API + MCP](https://www.anchorterminal.com/compare/groundmail-vs-postmark.md)
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- [Groundmail API + MCP vs SMTP2GO API + MCP](https://www.anchorterminal.com/compare/groundmail-vs-smtp2go.md)
- [Groundmail API + MCP vs Zoho CPaaS (formerly ZeptoMail)](https://www.anchorterminal.com/compare/groundmail-vs-zoho-zeptomail.md)
- [Loops API + MCP vs Resend API + MCP](https://www.anchorterminal.com/compare/loops-vs-resend.md)
- [MailerSend vs Resend API + MCP](https://www.anchorterminal.com/compare/mailersend-vs-resend.md)
- [Mailgun API + MCP vs Resend API + MCP](https://www.anchorterminal.com/compare/mailgun-vs-resend.md)
- [Mailjet API + MCP vs Resend API + MCP](https://www.anchorterminal.com/compare/mailjet-vs-resend.md)
- [Mailtrap Email API + MCP vs Resend API + MCP](https://www.anchorterminal.com/compare/mailtrap-vs-resend.md)
- [Mailchimp Transactional (Mandrill) vs Resend API + MCP](https://www.anchorterminal.com/compare/mandrill-vs-resend.md)
- [Postmark API + MCP vs Resend API + MCP](https://www.anchorterminal.com/compare/postmark-vs-resend.md)
- [Resend API + MCP vs Twilio SendGrid](https://www.anchorterminal.com/compare/resend-vs-sendgrid.md)
- [Resend API + MCP vs SMTP2GO API + MCP](https://www.anchorterminal.com/compare/resend-vs-smtp2go.md)
- [Resend API + MCP vs Zoho CPaaS (formerly ZeptoMail)](https://www.anchorterminal.com/compare/resend-vs-zoho-zeptomail.md)

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