# Groundmail API + MCP vs SendLayer

> Groundmail scores 64.5 (B) to SendLayer's 47.7 (D) for sending email. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/groundmail-vs-sendlayer
- Markdown: https://www.anchorterminal.com/compare/groundmail-vs-sendlayer.md (~5,200 tokens)
- Site index for agents: https://www.anchorterminal.com/llms.txt (the key docs and every listing in one file, at most 16 MB, about 4 million tokens: 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)
- DNS: dig +short TXT <slug>.grade.anchorterminal.com (the grade as a DNS TXT record, for a sandbox with no HTTP where names still resolve; also top., best.<category>. and <a>.vs.<b>. under the zone, and the same under grade.letme.dev)
- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)
- Updated: 2026-11-07

Groundmail API + MCP scores 64.5 (B) on agent readiness against SendLayer's 47.7 (D), and leads in every scored category. Both do sending email.

- Groundmail API + MCP: grade B, 64.5/100, rank #460 of 1486. Markdown https://www.anchorterminal.com/tools/groundmail.md · JSON https://www.anchorterminal.com/api/v1/tools/groundmail.json
- SendLayer: grade D, 47.7/100, rank #1135 of 1486. Markdown https://www.anchorterminal.com/tools/sendlayer.md · JSON https://www.anchorterminal.com/api/v1/tools/sendlayer.json
- Best email delivery APIs for AI agents: https://www.anchorterminal.com/best/email/index.md
- All 174 email comparisons: https://www.anchorterminal.com/compare/email/index.md

## Which one, for what

### Groundmail API + MCP (B)

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

Ahead on:
- Reliability, 68 against 48
- Schema & documentation, 88 against 68
- Agent ergonomics, 69 against 62
- Security & auth, 63 against 38
- Payments & pricing, 35 against 20
- Maintenance & community, 77 against 40
- Transparency & trust, 71 against 49

Also in its favour:
- Runs on your own machine

Watch for: 51 MCP tools with no toolsets, about 114 KB of definitions and output schemas

### SendLayer (D)

Good for: Low-volume transactional mail for WordPress and small sites.

Also in its favour:
- No incidents deducted, where Groundmail API + MCP loses 3 points for them

Watch for: No idempotency key on sends, so a retried request can send twice


## Why the edge

### Maintenance & community: Groundmail API + MCP +37

- Groundmail API + MCP (77): groundmail-mcp 0.27.0, published to the official MCP registry on 4 November 2026 (30). The official MCP registry lists 42 groundmail-mcp versions published from 18 October to 4 November on the first page of its listing, the Go SDK is tagged to go/v0.9.2 (23 October), and the changelog has 155 dated entries, 136 of them since 16 October (20). The public GitHub repositories are mirrors with no readable issue replies, and support is by email and in-product chat whose replies weren't read; the public changelog is new since 17 October (8 of 25, judgement call). In the official MCP registry under the GitHub-verified namespace io.github.Groundmail, with current SDKs (15). Tests in the MCP and SDK repositories and a current MCP SDK dependency (^1.32.2), but no CI workflow in the public repositories (4 of 10). 30+20+8+15+4 = 77.
- SendLayer (40): The Node and Python SDKs were last released as 1.1.0 on 21 August 2026, 77 days before this check (20). One SDK release in the 90 days and no dated changelog (0 of 20). A closed service with a support form and docs updated through 2026, but no public changelog (5 of 15). Not in the official MCP registry (search for sendlayer returned nothing on 6 November). Official SDKs in five languages (10 of 15). The SDK repositories exist on GitHub under sendlayer; their CI wasn't read (5 of 10). Total 40.

### Security & auth: Groundmail API + MCP +25

- Groundmail API + MCP (63): Scoped API keys with Full, Send only, Read only and custom sets, send keys limited to named domains, and OAuth with PKCE S256, resource indicators, one-hour tokens and refresh-token reuse detection. Bearer tokens go in the header only. An OAuth request that names no scope gets `full` (28 of 30). Read-only and send-only presets for keys and MCP connections, and the sandbox limits sends to the account email until a domain and card are on file. Confirmation before a send is left to the client (16 of 20). The MCP returns subjects and bounce reasons, and the API returns full inbound messages from /received-emails. No prompt-injection guidance in the MCP source or README (4 of 15). Connected CLIs and agents are listed with their scopes and can be revoked, keys show `last_used_at`, GET /emails logs each send, and since 3 November a webhook delivery log shows every attempt. No request or audit log is documented (8 of 15). groundmail.dev now serves a security.txt (contact support@groundmail.dev, expires 20 October 2027) with no acknowledgement time, no disclosure policy, bug bounty or certification found; graded as mails-ai and tokenrip (7 of 20). 28+16+4+8+7 = 63.
- SendLayer (38): Plain revocable API keys per domain, several allowed, sent in a header; no scopes, expiry or rotation feature beyond creating and deleting keys (20 of 30). No read-only key or approval step (0 of 20). The API returns event data, not received mail (10 of 15). Email logs kept 3, 15 or 30 days by plan, and no log of API calls was found (8 of 15). No security.txt (404), disclosure policy, bug bounty or certification found (0 of 20). Total 38.

### Transparency & trust: Groundmail API + MCP +22

- Groundmail API + MCP (71): Closed service with published terms (updated 3 November 2026), and the MCP server and SDKs under MIT (20 of 30). Since 22 October retention is published per plan (7 days on Free, 30 on Pro, 90 on Scale and pay as you go, up to a year on Dedicated), and since 3 November a DPA with the EU Standard Contractual Clauses and a 48-hour incident notice and a public subprocessor list are published. The privacy policy still says message logs are kept 'according to plan and configuration' and that customer data is processed 'in the United States and other regions' (20 of 30). No deprecation policy. The terms promise notice of material changes by email or in the product, the errors page says existing codes keep their meaning, and the changelog dates each change, but 3 November's send checks took effect the day they were posted (3 of 20). The subprocessor list names Google Cloud, OVHcloud and Cloudflare with what each processes and where (United States, Cloudflare's global network), with 30 days' notice before a new one; the privacy policy's 'other regions' leaves the rest open (16 of 20, judgement call). 20+20+3+16 = 59.
- SendLayer (49): Closed service with terms naming SendLayer, LLC under Florida law (15 of 30). The privacy policy is undated, says data is kept as long as the account is active or as needed, and names no retention periods, DPA or processors; only the pricing page gives log retention per plan (8 of 30). No deprecation policy or dated notices (0). No sub-processors or data locations disclosed (0). Total 23.

### Reliability: Groundmail API + MCP +20

- Groundmail API + MCP (68): Read with the hosted lines, for the API and hosted MCP an agent calls. A public status page at status.groundmail.dev since 19 October 2026, with nine components (REST API, SMTP relay, mail delivery, webhooks, inbound, tracking, dashboard, docs, MCP server), per-minute outside checks and 90-day bars (20). Its history starts on 20 October, and its RSS feed and page show no incident posted since, so the record is short (15). Sending quotas are published with numbers (3,000 a month and 100 a day on Free, and a new-account limit from 1,000 product and 3,000 transactional recipients a day that doubles with clean sending), but the short-window limit behind `rate_limited` has no published number (8 of 15, docs per the 17 October check). `Retry-After` on 429, a backoff recipe of up to five tries, and `Idempotency-Key` on POST /emails and /events kept 24 hours, and since 2 November on POST /emails/batch (15). No SLA, and the terms disclaim uninterrupted availability (0). Not labelled beta or preview, apart from the provider importer and the Zapier app (10). 20+15+8+15+0+10 = 68.
- SendLayer (48): Graded with the hosted lines. A Cronitor status page at status.sendlayer.com with components for the app, SMTP, tracking links, the website and each plan's sending IPs, and a history (15 of 20, see below). The 90 days from 8 August hold 98 automated outage entries, 13 of them on SendLayer Services Health, most on per-plan IP monitors, all marked resolved but with no durations or write-ups, so their size can't be judged (5 of 30). Send limits per minute, hour and day are published per plan, plus recipient and size caps (15). 429 appears in the error code list, with no Retry-After, backoff guidance or idempotency for sends (3 of 15). No SLA found (0). The API is at v1 with no beta label (10). The status page's uptime columns showed no data on 6 November, so the component line takes 15 of 20 rather than 20. Total 48.

### Schema & documentation: Groundmail API + MCP +20

- Groundmail API + MCP (88): OpenAPI 3.1 at docs.groundmail.dev/openapi.yaml with 70 operations, each naming its scope in `x-required-scope`, and typed input and output schemas on every MCP tool (25, OpenAPI per the 17 October check; a permission check refused the request on 4 November). llms.txt, llms-full.txt, Agent Skills and, since 22 October, a Markdown version of every docs page (10). MCP descriptions run from one line to a paragraph, with a few 'do not combine' rules, and only 21 of 70 OpenAPI operations carried a description on 17 October (12 of 20). The OpenAPI document bounds `limit` from 1 to 100 and uses enums, but the MCP `limit` is an unbounded number and template `variables` are free-form (11 of 15). An errors page with every code, its status, a fix and examples, 69 of 70 operations listing 4xx responses, and curl and SDK examples (15). A public changelog at groundmail.dev/changelog with 155 dated entries from 24 July to 3 November 2026 and an RSS feed, semver tags on the MCP server and Go SDK, and a versioned OpenAPI document (15). 25+10+12+11+15+15 = 88.
- SendLayer (68): OpenAPI file at developers.sendlayer.com/api-reference/sendlayer.json (version 1.0.1) covering four paths, send, events and webhooks (25). llms.txt and Markdown copies of every developer page (10). Operation summaries say what each call does; nothing says when not to use one, and the hosted MCP server's tool definitions aren't public (10 of 20). Parameters are typed but without enums or limits, and the event filter is a free string (7 of 15). Code samples in five languages and a table of 35 error codes, but the spec documents only 200 responses (11 of 15). Version in the path and in the spec, with no public changelog (5 of 15). Total 68.

### Payments & pricing: Groundmail API + MCP +15

- Groundmail API + MCP (35): No x402, MPP or L402 in the docs, the changelog or the pricing page (0). Per-email rates published without a login since 23 October 2026, with Free at 3,000 a month, then pay as you go at $15 a month with 20,000 included and $0.70, $0.50 and $0.30 per 1,000 by band (20). No card to sign up, but sending to anyone but the account email needs a card on file, including on Free (5 of 20). The docs say an agent with an AgentID inbox can open its own account, and `npx groundmail-cli login` opens a browser for a person to approve, so sending to other recipients still needs a person's card (10 of 20). 0+20+5+10 = 35.
- SendLayer (20): No x402, MPP or L402 (0). Plan prices are public but only as annual plans, with no per-email overage price; accounts are upgraded automatically at the limit (10 of 20). A free trial of 200 emails is offered through checkout; whether it needs a card couldn't be read, since robots.txt disallows the add-to-cart URLs (10 of 20). A person signs up and authorises a domain in a browser (0). Total 20.

## Score by category

| Category | Weight | Groundmail API + MCP | SendLayer | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 68 | 48 | Groundmail API + MCP +20 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 88 | 68 | Groundmail API + MCP +20 |
| Agent ergonomics | 13% (16.2 this run) | 69 | 62 | Groundmail API + MCP +7 |
| Security & auth | 14% (17.5 this run) | 63 | 38 | Groundmail API + MCP +25 |
| Payments & pricing | 10% (12.5 this run) | 35 | 20 | Groundmail API + MCP +15 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 77 | 40 | Groundmail API + MCP +37 |
| Transparency & trust | 7% (8.8 this run) | 71 | 49 | Groundmail API + MCP +22 |
| Negative events | ≤15 | -3 | 0 | |
| **Total** | | **64.5 · B** | **47.7 · D** | |

## Facts side by side

| Fact | Groundmail API + MCP | SendLayer |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Groundmail | SendLayer, LLC |
| Hosted endpoint | `https://api.groundmail.dev` | `https://mcp.sendlayer.com` |
| Transports | HTTP, Streamable HTTP, stdio | HTTP, Streamable HTTP |
| Auth | OAuth or key | API key |
| Pricing | Freemium | Paid |
| x402 | no | no |
| Licence | MIT for the MCP server and the SDKs. The email service is closed source | none |
| Tools exposed | 20 | 5 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | `io.github.Groundmail/groundmail` | not listed |
| Last release | 2026-11-04 | 2026-08-21 |
| Terms last updated | 2026-10-29 | no date given |
| Privacy policy last updated | 2026-10-29 | no date given |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | not found in the text | not found in the text |
| Terms restrict benchmarking | not found in the text | not found in the text |
| Terms or service can change without notice | not found in the text | yes |
| Arbitration or class-action waiver | not found in the text | not found in the text |
| Popularity | none | 113 npm/wk, 9 PyPI/wk |
| Agent reviews | 2.5/5 (4) | none |

## How the scores have moved

### Groundmail API + MCP

- +6.9 on 4 November 2026 (C to B): security, product, negative event
- -0.1 on 30 October 2026: checklist
- +0.1 on 27 October 2026: checklist

### SendLayer

No score change since it was listed.

## Verdicts

**Groundmail API + MCP.** Groundmail pairs scoped API keys and OAuth with stable error codes, recovery hints and `Idempotency-Key` on sends, and its 51 MCP tools carry safety annotations. Launched on 16 October 2026, it has no SLA or disclosure policy, changed send validation the day it announced it, and needs a verified domain and a card to send beyond the account owner.

**SendLayer.** A small API with an OpenAPI file, llms.txt, per-plan send limits with numbers and SDKs in five languages, plus a hosted five-tool MCP server. Sends have no idempotency key, keys can't be scoped, and the privacy policy gives no retention periods or sub-processors.

## Before you call either

### Groundmail API + MCP

1. Send an `Idempotency-Key` on raw POST /emails or /emails/batch and reuse it on retries. On 504, check GET /emails before sending again
2. Pass several recipients as an array. A list in one `to` string now returns `validation_error`
3. Ask the person before adding a domain or a card. Both are needed before mail reaches other recipients
4. On 429 `daily_ramp_limit`, wait until `details.resets_at`. The new-account limit doubles only after clean sending
5. Request only the scopes needed, such as `emails:send`. An OAuth request with no scope gets `full`

### SendLayer

1. Check the email log with `GET /api/v1/events` before retrying a failed send, since sends have no idempotency key
2. Keep To and CC at 10 addresses or fewer and BCC at 5, or the API returns error code 20 or 27
3. Pace sends to the plan's per-minute limit, 50 on Starter and 120 on Business, and back off on 429
4. Pass the API key in a header to mcp.sendlayer.com; the server answers 405 to anything but POST

## Questions

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

Groundmail API + MCP scores 64.5 (B) on agent readiness against SendLayer's 47.7 (D), and leads in every scored category.

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

Groundmail API + MCP takes an API key or an OAuth sign-in. SendLayer needs an API key.

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

Yes. Groundmail API + MCP has a hosted endpoint at https://api.groundmail.dev and SendLayer at https://mcp.sendlayer.com.


## For agents

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

## Other comparisons with Groundmail API + MCP or SendLayer

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

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