Resend pricing explained, and when your agent needs an inbox

Resend's transactional plans start free at 3,000 emails a month, then Pro costs $20 a month for 50,000 emails and Scale starts at $90 a month for 100,000. Every plan also includes 3 inboxes, extra inboxes are $1 each per month on paid plans, and every email an inbox sends or receives comes out of the same transactional quota. The figures below are as of 27 October 2026, from resend.com/pricing.

The second half of this post is about agents. If yours only sends, a sending API is all you need. If it has to read mail, keep threads and wait for a person to approve replies, you're choosing an inbox, and the pricing works differently.

What do Resend's transactional plans cost?

Resend prices transactional email by monthly volume. These are the tiers listed on its pricing page:

Overage is opt-in. You turn on pay-as-you-go under "Transactional Overages" and Resend bills each extra bucket of 1,000 emails at your plan's rate. If you leave it off and go over, Resend tells you and offers an upgrade. Billing is monthly only, with no annual discount. There's no free trial, because the Free plan doesn't expire. Registered nonprofits can apply for 50% off paid plans.

What does each tier include?

From the plan comparison:

• Free: 100 emails a day, 3 custom domains, 3 inboxes, 1 webhook endpoint, 30-day data retention, ticket support, 5 AI credits a month.
• Pro: no daily limit, 10 domains, 5 webhook endpoints, 100 AI credits a month and deliverability recommendations. More domains are a $20 a month add-on for 100 more.
• Scale: 1,000 domains, 10 webhook endpoints, 500 AI credits, a dedicated Slack channel and an urgent response SLA. Dedicated IPs ($30 a month, for senders over 3,000 emails a day) and SSO ($150 a month) are add-ons.
• Enterprise: custom volume, a 99.99% uptime SLA, a dedicated CSM, SSO and dedicated IPs included, and flexible retention.

Every plan gets the REST API, SMTP relay, the SDKs, scheduled and batch sending, open and link tracking, inbound email, signed webhooks and API key permissions. Data retention is 30 days on Free, Pro and Scale. The API rate limit is the same on every plan, so upgrading doesn't raise it.

What about marketing email?

Marketing plans are priced by contacts, not sends. Free covers 1,000 contacts. Pro Marketing runs from $40 a month for 5,000 contacts to $650 a month for 150,000. Broadcasts don't count against your transactional quota, and they can only go to existing contacts. Most agents won't touch this side of Resend.

How are inbound mail and inboxes billed?

Resend can receive mail in two ways. Receiving parses inbound mail for a domain and posts it to your webhook. Inboxes go further: Resend stores the mail and groups it into threads, with labels, drafts and folders, through the dashboard, API, CLI and MCP server.

Both use the transactional quota. The pricing page says "each received email counts towards your transactional emails quota", and inboxes "do not come with a separate email allowance". Every plan includes 3 inboxes. Paid plans with pay-as-you-go add more at $1 an inbox a month. The Free plan stops at 3.

An inbox needs a verified domain with receiving turned on, or forwarding from an address you already have.

Does your agent need a sending API or an inbox?

If the agent sends password resets, receipts or alerts and nobody replies, you want a sending API, and Resend is a strong one. Volume pricing, SMTP, React Email and dedicated IPs are all built for that.

An agent that answers email needs more than that:

• Receive: mail arrives at an address the agent owns, and your code hears about it straight away.
• Threads: the agent replies in the same conversation, and can read the history first.
• Drafts: the agent writes, and a person decides what goes out.

Resend Inboxes now do all three. So the question is less about features and more about how you want to pay, and how tightly you want to limit what the agent's key can do.

How does ACK's pricing compare?

ACK is one plan: $19 per organisation per month, with 10 inboxes included and $2 a month for each extra inbox. Every feature is on that plan. There's no per-email meter. Each inbox can send 1,000 emails a month at full speed, then sending slows until the next month. You're never charged for more, and receiving carries on as normal.

Some rough monthly costs, using only the published prices:

On Resend, the $20 Pro plan covers 50,000 emails across sending and receiving. ACK's fair-use limit counts sends only, at 1,000 per inbox a month. If your agents mostly read and reply one to one, ACK's flat price is easy to predict. If you send at high volume, or want marketing email in the same account, Resend's tiers fit better. At 25 inboxes, Resend costs less.

ACK has a 14-day trial. It needs a card, trial inboxes use a shared ACK address, and you can send 100 emails in total. Resend has no trial, but its Free plan doesn't end.

Can the agent write drafts but not send them?

This is the biggest difference for an agent that needs approval.

Resend's API key docs list two permissions. full_access can do anything. sending_access "can only send emails. For Inboxes, it can call only Reply to Thread Email, Forward Thread Email, Create Draft and Send Draft." You can restrict a sending key to one domain, and then it can only use that domain's inboxes. Resend's built-in Inbox agent never sends on its own and saves replies as drafts. If you bring your own agent, the key decides.

Here's how Resend creates a draft, from its drafts docs:

curl -X POST 'https://api.resend.com/inboxes/b3e2b2b6-3f0e-4c8e-9ad3-2f43a1e2c7f1/drafts' \
     -H 'Authorization: Bearer re_xxxxxxxxx' \
     -H 'Content-Type: application/json' \
     -d $'{
  "to": ["ada@example.com"],
  "subject": "Refund for order 1041",
  "html": "<p>Refund issued for order 1041.</p>",
  "text": "Refund issued for order 1041."
}'

ACK keys can be scoped to the organisation, a pod of inboxes or a single inbox, and you choose each permission. This key can read one inbox and write drafts there, and nothing else:

curl https://api.ack.now/v0/inboxes/support-agent@trial.ack.now\
/api-keys \
  -H "Authorization: Bearer $ACK_API_KEY" \
  --json '{"name": "support-agent, drafts only",
           "permissions": {"inbox_read": true, "message_read": true,
                           "draft_read": true, "draft_create": true,
                           "draft_update": true}}'

If the agent tries to send, the request fails with a 403. A person reads the draft in the app and clicks Send. Approve your agent's email before it goes out walks through it.

FAQ

Does Resend have a free plan?

Yes. The Free plan includes 3,000 emails a month, up to 100 a day, 3 domains and 3 inboxes, with 30-day data retention.

Do received emails count against my Resend quota?

Yes. Each received email counts towards your transactional quota, and so does every email sent or received through an inbox.

What happens if I go over my Resend quota?

With pay-as-you-go on, you pay your plan's overage rate per 1,000 emails, from $0.90 down to $0.46. Without it, Resend notifies you and offers an upgrade.

Does ACK charge for overage?

No. Each inbox can send 1,000 emails a month at full speed. After that, sending slows until the next month, and nothing is added to your bill.

Can my agent use MCP with either one?

Yes. Resend runs a remote MCP server at https://mcp.resend.com/mcp. Connecting signs in with OAuth, or you can pass an API key as a Bearer token. ACK's is at https://mcp.ack.now/mcp and takes an API key in an x-api-key or Authorization header. Add an email MCP server to your agent covers the setup.

Try it

If your agent needs its own inbox, start the 14-day trial, make a drafts-only key, and follow How to give an AI agent its own email address. The developer docs cover the rest of the API.