The best email API for an AI agent depends on whose mailbox it works in. For agents that work in your own or your team's Gmail, Outlook, and IMAP mailboxes, use Fluxmail, which gives you one API and MCP server for all of them, hosted or self-hosted, at a flat price. For a product whose customers connect their own email, calendar, and contacts, use Nylas. For agents that need new inboxes of their own, use AgentMail. EmailEngine is the self-hosted choice for connecting many accounts with webhooks, and Composio fits when email is one of many apps.
Details below come from each product's docs and pricing pages, checked October 23, 2026. We make Fluxmail, so it's listed first.
What should I look for in an email API for agents?
There are three kinds of email API, and they solve different problems:
- Some connect existing mailboxes, so the agent reads and sends from a real person's Gmail or Outlook account. Fluxmail, Nylas, EmailEngine, and Composio work this way.
- Some create new inboxes, so the agent gets its own address and receives mail by webhook. AgentMail works this way.
- Sending APIs such as Resend, Postmark, Mailgun, and Amazon SES send mail from your domain, often with inbound routing, but they don't connect to anyone's existing Gmail or Outlook inbox. Use one when your agent sends notifications or outreach from an application address.
This list covers the first two. Once you know which you need, compare interfaces (MCP for AI clients, REST for your code), hosting, how much Gmail and Microsoft setup you have to do yourself, and how the price grows with accounts.
What are the best email APIs for AI agents?
1. Fluxmail
Fluxmail connects agents to Gmail, Google Workspace, Microsoft 365, Outlook, Exchange, and IMAP mailboxes through one set of operations. Fluxmail Cloud serves them two ways: an MCP server at https://cloud.fluxmail.ai/mcp for Claude, ChatGPT, Cursor, and other AI clients, and a REST API with scoped agent keys for your own code. Operations cover search, threads, drafts, send, reply, forward, attachment downloads, labels, folders, archive, and trash, and they work the same way on every provider. Fluxmail is email only, with no calendar, contacts, or inbound webhooks.
Each OAuth connection or agent key is limited to the mailboxes and scopes you pick, such as read-only, drafts without sending, or full mail access. Sends take an idempotency key, so a retried request doesn't send the same message twice. Cloud connects Gmail through Fluxmail's own Google app, which has completed Google's security assessment. It doesn't store messages.
Self-hosted Fluxmail runs the same email operations and permission scopes on your machine or in Docker, with credentials kept on your server, plus a CLI and scheduled sending. Its versioned REST API uses different routes and request fields from Cloud's, so code written for one needs changes to call the other. Its bundled Google client means local Gmail setups don't need a Google Cloud project.
Self-hosted is free for one member and three mailboxes. Pro is $15 a month for ten mailboxes and Business is $25 per member a month, in Cloud or self-hosted, with no per-call charges.
2. Nylas
Nylas is a hosted API for products whose customers connect their email, calendar, and contacts. It has webhooks, SDKs, US and EU regions, scheduling, and meeting notes, plus Agent Accounts that create inboxes on your domain. Its MCP server authenticates with a Nylas API key and works with accounts already connected to Nylas.
For Gmail, you use your own Google Cloud project, or Nylas's shared Google app on annual Pro with Accelerator or an Enterprise add-on. With your own project, reading Gmail needs Google's verification and a security assessment, unless the app is for personal use with fewer than 100 users or internal to your Workspace.
Nylas prices by connected account. The free tier covers 5 accounts. Essentials is $15 a month for 10 accounts, then $2.25 each, and Pro is $49 a month for 25, then $2.00 each. See Fluxmail vs Nylas and Nylas alternatives for AI agents.
3. AgentMail
AgentMail gives each agent its own inbox. An API call creates an address on agentmail.to or, from the Developer plan up, your own domain. New mail arrives by webhook or WebSocket, and a hosted MCP server lets AI clients use the inboxes directly. It's a good fit for a support agent with its own address, or an agent that signs up for services and reads verification codes. It doesn't document connecting existing Gmail or Outlook mailboxes.
It's free for 3 inboxes and 3,000 emails a month. Developer is $20 a month for 10 inboxes and Startup is $200 a month for 150. See Fluxmail vs AgentMail.
4. EmailEngine
EmailEngine is a self-hosted email gateway for apps that connect many accounts. Besides IMAP and SMTP, it talks to Gmail and Microsoft accounts through native Gmail API and Microsoft Graph integrations. When mail arrives or changes, it sends signed webhooks, and it also queues outgoing mail and supports templates and mail merge. You'll need Redis to run it. An MCP endpoint has been in beta since August 2026 and is off until an administrator turns it on.
After a 14-day trial, it costs $1,450 a year, excluding VAT, for unlimited instances and accounts. See Fluxmail vs EmailEngine.
5. Composio
Composio is a hosted integration platform. Its Gmail toolkit has 63 tools and its Outlook toolkit has 328, including calendar and contacts, alongside a large catalog of other apps. It manages OAuth for your users, gives each one a hosted MCP URL, and has SDKs and Gmail event triggers. Gmail and Outlook use different tools, so code that works with both handles two schemas.
With your own OAuth app, the free Hobby plan includes 100,000 tool calls a month. Pro is $29 a month including $29 of usage, then $0.0003 per call with your own OAuth app or $0.0005 with Composio's managed apps. See Fluxmail vs Composio Gmail.
6. The Gmail API and Microsoft Graph directly
You can skip a middle layer and call the Gmail API and Microsoft Graph yourself. Both are free to use within their quotas and give you every feature the provider has. In exchange, you take on two OAuth apps, token storage and refresh, two different data models, and, for Gmail, Google's verification and security assessment once your app reads other people's mail. Use them directly when you only support one provider or need a feature no wrapper exposes. For IMAP mailboxes such as iCloud or Fastmail, you'd add an IMAP and SMTP library on top.
How do they compare?
| API | Mailboxes | Hosting | MCP | Price |
|---|---|---|---|---|
| Fluxmail | Your existing Gmail, Outlook, Exchange, IMAP | Hosted or self-hosted | Yes | Free self-hosted plan; Pro $15 a month for 10 mailboxes |
| Nylas | Your customers' accounts, plus Agent Accounts | Hosted | Yes, with a Nylas API key | Free for 5 accounts; from $15 a month plus per account |
| AgentMail | New inboxes it creates | Hosted | Yes | Free for 3 inboxes; Developer $20 a month |
| EmailEngine | Many existing accounts | Self-hosted | Beta | $1,450 a year |
| Composio | Your users' Gmail and Outlook, plus other apps | Hosted | Yes | Free tier; Pro $29 a month plus usage |
| Gmail API and Graph | One provider each | Provider-hosted | No | Free within quotas |
Frequently asked questions
What's the difference between an email API and an email MCP server?
Your code calls an email API. An MCP server exposes the same kind of operations as tools that AI clients such as Claude, ChatGPT, and Cursor can call on their own. Several products on this list offer both. In Fluxmail, MCP connections and REST agent keys use the same permission scopes. For a list focused on MCP, see The best email MCP servers for AI agents.
Should my agent use its own inbox or mine?
Give it its own inbox when it acts as a separate identity, such as a support address or a bot that signs up for services. Let it use yours when it's working for you: triaging your inbox, drafting replies from your address, or pulling invoices from your mail. Some setups use both, with AgentMail for the agent's public address and Fluxmail for a person's inbox.
Which email API is cheapest for a few mailboxes?
For a handful of your own mailboxes, self-hosted Fluxmail is free for three, and Fluxmail Pro covers ten for $15 a month. Nylas is free for five accounts, and AgentMail is free for three inboxes it creates. At larger scale the pricing models differ: Nylas adds a fee per account, Composio charges per tool call past its allowance, and EmailEngine is one flat yearly price.
How do I stop an agent from sending mail it shouldn't?
Give it the narrowest permission that works. With Fluxmail, an agent key or OAuth connection can be read-only, or allowed to write drafts but not send. Treat incoming mail as untrusted input, because a message can contain instructions aimed at the agent. How to give an AI agent access to your inbox safely covers this in detail.