Best Email for AI Agents: Compare Inboxes, APIs and Prices

The best email service for an AI agent depends on whose inbox it needs. For a new address the agent can work from, start with Robotomail or AgentMail. For an agent working inside an existing Gmail or Outlook account, use that provider's API. If your application already uses Resend, its receiving and inbox features are worth considering before adding another service.

Our recommendation: choose Robotomail for a personal agent that needs its own custom-domain address at $5/month, with ready-made MCP setup and a REST API. Choose AgentMail if a larger free allowance or several custom domains on its entry paid plan matter more.

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The shortlist

We build Robotomail. This guide compares documented product capabilities and public prices; recommendations depend on the workload. Prices were checked on 3 November 2026.

Robotomail: a small paid plan for an agent's own address

Robotomail gives the agent a mailbox it can use through MCP, the REST API or the CLI. The same address receives replies when you change the model or runtime. Messages and threads stay in the mailbox, so the application can load the conversation before generating its next response.

Solo costs $5/month and includes 1 mailbox; 500 sends / month; 50 sends / day; 500 inbound / month; 1 custom domain; 1 GB storage. It is a practical starting point for one personal or project agent. Starter is $19/month and includes 10 mailboxes, with separate sending and incoming allowances. See all plan limits.

For an existing agent, use the OpenClaw, Hermes or Claude Code instructions. MCP signs in through your browser and provides tools to read, send and reply. Use the API for attachments, HTML messages, mailbox provisioning and domain management.

Choose it when: you want one small, paid inbox on your domain, or the Robotomail setup fits your agent. Consider another option when: your priority is a large free allowance or operating inside a person's existing Gmail mailbox.

AgentMail: more room on Free and more domains on Developer

AgentMail is another dedicated agent-inbox service. Its public Free plan includes three inboxes, 3,000 emails/month and 3 GB of storage. Developer is $20/month for ten inboxes, ten custom domains and 10,000 emails/month. That makes it worth considering for a larger prototype or a project serving several domains. AgentMail pricing.

It documents message and thread APIs, attachments, MCP, webhooks and WebSockets. These are overlapping capabilities with Robotomail, rather than reasons to claim that only one service can handle a conversation. See its event interfaces and our AgentMail comparison.

Choose it when: the free capacity, domain allowance or its integrations fit your project. Choose Robotomail Solo when: one custom-domain mailbox is enough and you prefer the smaller monthly commitment.

Resend: keep an existing application in one email stack

Resend supports incoming email, webhook notifications, message retrieval, attachments and threaded replies. It also offers inboxes with thread and agent access. It should not be described as a send-only service. Receiving documentation.

Its Free transactional plan includes 3,000 emails/month and a 100-email daily limit. Pro starts at $20/month for 50,000 emails. Three inboxes are included; paid plans can add more at $1 per inbox per month. Inbox sending and receiving both count toward the transactional email quota. Resend pricing.

Choose it when: your application already uses Resend and its inbox or receiving interface covers the agent workflow. Compare the actual quota and setup with a dedicated agent-mailbox product before moving an existing integration.

Gmail API and Microsoft Graph: work inside an existing inbox

Use the Gmail API when the agent needs a person's existing Gmail address or conversations. Use Microsoft Graph for an existing Outlook or Microsoft 365 mailbox. A new agent mailbox would not automatically inherit that address, history or organizational access.

The price depends on the underlying account or workplace plan. Account creation, permissions and ongoing administration are separate from sending a message through an API. Gmail API overview · Microsoft Graph mail overview.

Choose them when: the existing mailbox is a requirement. Choose a dedicated agent inbox when: the agent should have a separate address and start its own conversations.

Already using SendGrid, Mailgun or Postmark?

These services also have incoming-mail interfaces: SendGrid Inbound Parse, Mailgun routes and Postmark inbound webhooks.

Keep an existing integration if it already handles your workflow well. When adding an agent, check how you will identify its incoming address, retrieve earlier messages and continue a thread. A dedicated inbox can simplify that work, but receiving email is not unique to agent-mailbox services.

Try one complete conversation

The useful test is a message that gets a reply and then a follow-up. For example, email the agent a project question, have it ask for a missing detail, and answer that question from your own inbox.

1. Choose an address. Create a Robotomail account and verify your email. Use the included mailbox for the first test.
2. Connect the agent. Open Connections and choose your client, or follow the API quickstart.
3. Send the first request. Email the agent from your verified address. Ask it to read the message and draft a reply.
4. Approve a reply. Check the sender, message and recipient. Then ask the agent to reply and confirm that it arrives in the same thread.
5. Continue the conversation. Send another reply and ask the agent to explain what changed. It should use the earlier messages as context.

1 mailbox, 10 sends and 10 receives per month. Exchange mail only between your agent and your verified email address. Upgrade to email anyone. No credit card, no expiry. Allowances reset on the first of each month (UTC). Upgrade for higher limits or a custom domain.

MCP provides tools the agent can call; it does not keep a stopped runtime running. For an unattended agent, use a persistent runtime and an inbound event or polling loop. The receive-and-reply guide covers that application pattern.

Questions before you choose

What is the best email API for AI agents?

For a new agent-owned address, compare Robotomail and AgentMail against your mailbox count, domain count and expected conversations. Consider Resend when you already use its application email stack. Use Gmail or Graph when the agent must work in an existing user's inbox.

Can I connect an agent without writing an email integration?

Yes. A compatible MCP client can connect to Robotomail, sign in through the browser and discover its email tools. Start with the MCP setup guide. Your agent still needs instructions about what to read and when to send.

Can I send attachments through MCP?

Robotomail's current MCP tools handle plain-text email. Use its REST API for attachments and HTML messages. The tool reference lists the supported operations.

Will switching providers transfer old conversations?

No. Creating a new mailbox or changing domain routing does not copy message history. Keep access to the old store or plan a separate import before moving a workflow that depends on earlier messages.

Can I use my own domain?

Robotomail Solo and higher plans include custom-domain support. Add the domain, publish its DNS records and verify it. If staff already use the parent domain, a dedicated agent subdomain lets you keep their existing mail route.

Create your agent's mailbox · Choose an integration · Compare plans