Resend Inboxes for AI Agents vs Mermail: Compared
Resend just launched Inboxes for AI agents. A fair side-by-side with Mermail on pricing, MCP access, agent permissions, approvals and payments, plus when to pick each.
By Toan Nhu
Resend just launched Resend Inboxes, an agent email inbox API that gives agents and teams a shared, threaded inbox on your own domain. It fits teams that already send with Resend and want people and agents working the same support or ops inbox; Mermail fits builders who want each agent to own its inbox and, when needed, a user-controlled wallet to pay.
Below is a side-by-side look based only on Resend's announcement and Mermail's own docs, so you can pick the right email inbox for AI agents without guesswork.
What Resend announced
Resend started with sending and added receiving in 2025. Their announcement is candid about what that left to you: webhooks fire, but reading, sorting, replying and remembering the conversation was still your job, and increasingly that job falls to an agent. Inboxes is their answer:
- An inbox sends and receives at an address on your domain, and every message is grouped into a thread your app, team and agents can reach.
- Primitives for folders, Gmail-style search, labels, drafts, forwarding and reply all, plus webhooks such as a received email or an assigned thread.
- Agents like Claude Code, Cursor, Codex, Grok or Gemini connect through an MCP server, skills or the CLI.
- A built-in agent takes instructions, a tone and a list of allowed actions. Resend suggests starting with drafts and labels and widening scope as trust grows.
- Start free with up to 3 inboxes; extra inboxes on paid plans are $1 each, pay-as-you-go.
When a major email provider ships inboxes for agents, it validates the category. A sending pipe is not enough for an agent that signs up for services, waits on replies and carries conversations over days. If you are evaluating providers for that inbound side, run through our inbound checklist for AI agents.
Resend Inboxes vs Mermail at a glance
| Resend Inboxes | Mermail | ||
|---|---|---|---|
Pricing | 3 free inboxes, then $1 per inbox on paid plans (paid plan price not in the announcement) | Free: 1 inbox. $19/mo: 5 inboxes. $49/mo: 10 inboxes. Custom domains from $19 | |
Access | API, CLI, MCP server and skills, SDKs in many languages | MCP over Streamable HTTP with OAuth or API key, plus API, CLI and Agent Skills | |
Mail handling | Threads, folders, labels, drafts, search, reply all, forwarding, webhooks | Search, threads, drafts and send (MCP tools include search_emails, save_draft, send_email) | |
Built-in agent | Configurable instructions, tone and allowed actions (draft, label, assign, forward, archive, spam, delete) | Mailbox agent that can search, draft and triage | |
Team use | Shared inboxes, assignment and notes | Team members on paid plans | |
Approval | You choose which actions the built-in agent can take | Email effects need explicit authorization; save_draft stores a draft for review | |
Payments | Not mentioned in the announcement | Agent Wallet via PayBox, including x402 payments and receipts |
When to pick Resend Inboxes
- You already send with Resend and want inbound on the same platform and domain.
- Your main use is a shared team inbox: support, recruiting or on-call, where people and agents work threads side by side with assignment and notes.
- You want a built-in agent with configurable instructions, tone and a defined set of allowed actions.
- You run many inboxes and per-inbox pricing suits you.
When to pick Mermail
- Each agent should own its address for registrations, verification codes, receipts and ongoing conversations.
- You want one MCP connection that covers both email and payments, so an agent can sign up and then pay inside limits you set.
- You want drafts saved for review and explicit authorization before email effects happen.
- Plan-based pricing with bundled email volume, storage and API limits fits your budget better than per-inbox billing.
Not sure how your agent should connect? Our guide to MCP vs SDK vs API for agent email and the roundup of email MCP servers compared walk through the trade-offs. Whichever you choose, test the agent's judgment before widening its permissions, as covered in how to evaluate an email agent's judgment. For a wider look, see Mermail vs Resend vs AgentMail.
How Mermail fits
Mermail is built as privacy-first email inboxes for AI agents. According to the Mermail docs, your agent gets a dedicated inbox on a hosted address or verified custom domain, and connects to ChatGPT, Claude, Cursor, Codex or another compatible assistant through one MCP connection. Email effects require explicit authorization, and when the agent needs to pay, Agent Wallet via PayBox lets it pay one selected x402 resource without exposing private keys, inside the delegation and signing policy you configured.
To try it, create your first Mermail inbox and connect it to the assistant you already use.
FAQ
What are Resend Inboxes?
An inbox product from Resend, announced as built for agents and ready for teams. Each inbox sends and receives at an address on your domain, groups mail into threads and is available through the API, CLI and an MCP server.
How much do Resend Inboxes cost?
Per the announcement, you can start free with up to 3 inboxes, and additional inboxes on paid plans are $1 each, pay-as-you-go. The paid plan price itself is not listed in the announcement.
Is Mermail a Resend Inboxes alternative?
It can be, depending on the job. Mermail focuses on an agent-owned inbox plus a user-controlled Agent Wallet over one MCP connection, while Resend Inboxes is strong for shared team inboxes on the Resend platform.
Do both support MCP?
Yes. Resend offers an MCP server, skills and a CLI. Mermail offers MCP over Streamable HTTP with OAuth or an API key, plus an API, CLI and Agent Skills.
Can I review what an agent sends?
With Resend you choose which actions its built-in agent may take, such as only drafts and labels. With Mermail, email effects need explicit authorization, and save_draft stores a draft for review.
