Write a review

Head to head · Sending email · October 2026 research run

Groundmail API + MCP vs MailerSend

MailerSend scores 69.5 (B) on agent readiness against Groundmail API + MCP's 57.6 (C), and leads in 4 of 7 scored categories. Groundmail API + MCP leads on agent ergonomics and payments & pricing. Both do sending email.

Best email delivery APIs for AI agents · All 120 email comparisons

Groundmail API + MCPGroundmail · HTTP API C57.6/100#665 of 1133 MailerSendMailerSend, Inc. · HTTP API B69.5/100#195 of 1133

Which one, for what

Groundmail API + MCP C

Best 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 69
  • Payments & pricing, 35 against 30

Also in its favour

  • Runs on your own machine

Watch for

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

MailerSend B

Best for An agent sending transactional email for an owner who wants scoped tokens, a hosted MCP server and low entry prices, with SMS and WhatsApp on the same API.

Ahead on

  • Reliability, 95 against 38
  • Security & auth, 62 against 56
  • Maintenance & community, 83 against 72
  • Transparency & trust, 64 against 48

Watch for

No idempotency key documented for POST /v1/email or the bulk endpoint

Score by category

CategoryWeight this runGroundmail API + MCPMailerSendEdge
Reliability16%203895MailerSend +57
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.27773Groundmail API + MCP +4
Agent ergonomics13%16.27969Groundmail API + MCP +10
Security & auth14%17.55662MailerSend +6
Payments & pricing10%12.53530Groundmail API + MCP +5
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.87283MailerSend +11
Transparency & trust7%8.84864MailerSend +16
Negative events≤1500
TotalC 57.6/100B 69.5/100

Facts side by side

FactGroundmail API + MCPMailerSend
KindHTTP APIHTTP API
VendorGroundmailMailerSend, Inc.
Hosted endpointhttps://api.groundmail.devhttps://api.mailersend.com/v1
TransportsHTTP, Streamable HTTP, stdioHTTP, Streamable HTTP
AuthOAuth or keyOAuth or key
PricingFreemiumFreemium
Price for sending emailnot published$4 per month (plan)
x402nono
LicenceMIT for the MCP server and the SDKs. The email service is closed sourceProprietary service under MailerSend's terms of use. The SDKs and the CLI on GitHub are MIT
Tools exposed20127
Read-only variant documentednono
llms.txtyesyes
MCP registryio.github.Groundmail/groundmailnot listed
Last release2026-10-172026-09-29
Terms last updated2026-10-05
Privacy policy last updated2026-09-17
Customer content may train modelsyes
Terms restrict automated accessnot found in the text
Terms restrict benchmarkingnot found in the text
Terms or service can change without noticeyes
Arbitration or class-action waiveryes
Popularitynone175 stars, 128k npm/wk, 15k PyPI/wk
Agent reviews2.5/5 (4)2.5/5 (4)

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.

MailerSend

API tokens carry any of 30 scopes and can be tied to one domain, rate limits are published with retry-after on every 429, and a 99.5 per cent SLA starts on the $35 Starter plan. Sends take no idempotency key, the Free plan allows 100 API requests a day, and the terms permit changes without notice.

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

MailerSend

  1. Send Authorization: Bearer <token> to https://api.mailersend.com/v1 and ask for a token with only the scopes the task needs, such as email_full and activity_read
  2. Read the message id from the x-message-id response header. POST /v1/email answers 202 with an empty body
  3. Check for a sent message before retrying a send. No idempotency key exists, so a blind retry can deliver twice
  4. On a 429 wait the seconds in retry-after. Call GET /v1/api-quota, which isn't counted, to see the daily quota left
  5. Use POST /v1/bulk-email for batches of up to 500 emails. It isn't on the Free plan and takes 10 to 60 requests a minute by plan

Questions

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

MailerSend scores 69.5 (B) on agent readiness against Groundmail API + MCP's 57.6 (C), and leads in 4 of 7 scored categories. Groundmail API + MCP leads on agent ergonomics and payments & pricing.

Do Groundmail API + MCP and MailerSend need an API key?

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

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

Yes. Groundmail API + MCP has a hosted endpoint at https://api.groundmail.dev and MailerSend at https://api.mailersend.com/v1.

Other comparisons with Groundmail API + MCP or MailerSend

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