Email API for AI Agents: MCP Support, Free Plans and Entry Prices Compared
An AI agent that sends email needs more than an API: it needs an MCP server, a sign-in the human approves, safe retries and limits that stop a loop. This page compares four email services on what each vendor publishes about MCP support, its free plan and its entry paid plan, as read on November 13, 2026. We did not run the other vendors' MCP servers, so the table records only what their own pages say. AISend is newer, has no long sending history and is a paid service: an account needs an active plan, and a verified domain of your own, before it can send.
The comparison
| Service | MCP server (per the vendor's own pages) | Free plan | Entry paid plan |
|---|---|---|---|
| AISend | Hosted at api.aisend.app/mcp with OAuth sign-in or an API key, plus a local npm server (aisend-mcp); listed in the Official MCP Registry as app.aisend/aisend | None | $14/month, 50,000 emails |
| Resend | MCP server documented at resend.com/docs/mcp-server | 3,000 emails a month, 100 a day | Pro $20/month, 50,000 emails |
| Postmark | Official postmark-mcp server on GitHub, described there as 24 tools | 100 emails a month | Basic $15/month, from 10,000 emails |
| Elastic Email | MCP documentation on elasticemail.com | Up to 3,000 emails a month | Starter from $19/month, priced by volume |
What to look for when an agent does the sending
- A sign-in the human approves and can revoke. AISend uses OAuth 2.1 with PKCE: the owner presses Approve on a consent screen, and the connection is an API key that expires after 90 days and can be revoked on the API Keys page.
- Tool annotations. AISend marks send_email destructive and the status and list tools read-only, so clients that confirm tool calls ask before a send.
- Safe retries. AISend requires an idempotency_key on send_email and returns the first result for a repeated key.
- Limits that stop a loop. An AISend assistant connection is capped at 100 emails a day, and plan caps, new-account ramp-up and domain caps apply to every send.
- Errors an agent can act on. AISend returns 402 with code paid_plan_required or subscription_inactive when an account cannot send, 429 for quotas and rate limits and 409 for a reused idempotency key.
- A way to review the work. Every sent email and its status is listed on the AISend Emails page.
We have not checked whether the other services offer the same controls; read their documentation before you hand an agent a send tool. The AISend MCP page has the full agent quickstart, and How to Let an AI Agent Send Email Safely covers the controls in detail.
Where AISend is not the right pick
- You want a free plan to try the integration: Resend, Postmark and Elastic Email each list one and AISend does not.
- You send marketing campaigns: AISend is for transactional and consented mail only.
- You need a long sending history: AISend is newer than the others here.
Frequently asked questions
Which email API has an MCP server for AI agents?
As read on November 13, 2026, AISend, Resend, Postmark and Elastic Email each publish an MCP server or MCP documentation. AISend's is hosted with OAuth sign-in and also runs locally through npx aisend-mcp. We did not test the others.
Can ChatGPT or Claude send email through AISend?
Yes. Add https://api.aisend.app/mcp as a custom connector, sign in to AISend and press Approve. The account needs an active plan and a verified sending domain to send to other people.
Is it safe to let an AI agent send email?
Only with controls: human approval before sends, a verified domain, daily caps, idempotency keys and a key you can revoke. AISend enforces the caps, the verified-domain rule and the idempotency key; whether a client asks for confirmation before each send is the client's setting.
Sources
More guides
Connect an assistant to AISend
Hosted MCP with OAuth sign-in. AISend is a paid service: an account needs an active plan before it can send.