AgentMail alternative: how ACK compares

AgentMail is an email API for AI agents: you create inboxes over an API, and your agent sends, receives and replies from them. If you're looking for an AgentMail alternative, ACK does the same core job with a different shape: one $19 plan per organisation with 10 inboxes and every feature, and mail stored in the EU.

This page covers what AgentMail does well, where ACK differs, and a side-by-side table. Every AgentMail fact here comes from AgentMail's own pricing page and docs, checked on 27 October 2026. Prices and limits change, so check their pages before you decide.

What is AgentMail?

AgentMail describes itself as "the first email provider built for AI agents". Its introduction lists inboxes, threads, messages, webhooks and WebSockets, plus automatic labelling with your own prompts, full-text search and structured data extraction.

The quickstart uses SDKs for Python and TypeScript, and there's a CLI. Creating an inbox and sending from it looks like this in Python, copied from that page:

from agentmail import AgentMail
import os
from dotenv import load_dotenv

load_dotenv()
client = AgentMail(api_key=os.getenv("AGENTMAIL_API_KEY"))
inbox = client.inboxes.create()
client.inboxes.messages.send(
    inbox.inbox_id,
    to="recipient@example.com",
    subject="Hello from AgentMail!",
    text="This is my first email sent with the AgentMail API."
)

What does AgentMail do well?

A fair amount, and you should know it before you switch.

• A free tier with no card. Their pricing page lists a Free plan with 3 inboxes, 3,000 emails a month (100 a day) and 3 GB of storage, no credit card required.
• Drafts for human review. The drafts docs say an agent can create a draft "which a human can then review and approve before it's sent", and drafts take a send_at time for scheduled sending.
• Scoped, whitelisted permissions. API key permissions grant only what you set to true, keys can be scoped to a pod or an inbox, and there's a separate draft_send permission.
• A big MCP server. The MCP server at https://mcp.agentmail.to/mcp has 47 tools, including calendar tools, and supports OAuth sign-in as well as an x-api-key header.
• More than webhooks. You can receive mail over WebSockets as well as webhooks, which are delivered and signed through Svix.
• Room to grow. The Startup plan includes a SOC 2 report, and Enterprise adds SSO, dedicated IPs and a white-label option.

If you want SDKs in Python or TypeScript, calendar tools or a free plan to try things without a card, those are real reasons to stay.

How is ACK different?

ACK is an email inbox for AI agents too. You create inboxes over a REST API at https://api.ack.now/v0 or through the MCP server at https://mcp.ack.now/mcp, and get told about new mail by signed webhooks. ACK is a separate product with its own API and docs.

The differences that matter most:

One plan instead of tiers

ACK's pricing is one plan: $19 per organisation per month, 10 inboxes included, $2 a month for each extra inbox. The REST API, MCP server, webhooks, your own domains, drafts, scoped keys, open tracking, mail import and team members are all on it. There's nothing held back for a higher tier.

Sending has a fair-use limit rather than a meter. Each inbox can send 1,000 emails a month at full speed. Past that, sending slows down until the next month, and you're never charged for more.

So 25 inboxes on ACK is $19 + 15 × $2 = $49 a month. On AgentMail, 10 inboxes is the $20 Developer plan; past that, their pricing page lists add-ons at $2 a month per inbox, per domain or per 1,000 emails, or the $200 Startup plan with 150 inboxes.

Mail stays in the EU on every plan

ACK stores mail, attachments and the database in the EU, in Amazon Web Services' Stockholm region (eu-north-1). That's the same on the $19 plan as on any other, and it's set out on the privacy page. AgentMail's pricing page lists "EU region cloud" under the Enterprise plan.

Drafts-for-approval, enforced by the key

Both products let an agent save a draft for a person to send. In ACK, the drafts-only key is the whole point: give the agent a key without send permissions and a send, reply or forward fails with a 403, even if an email talks the agent into trying. Drafts show up on the inbox's Drafts page in the app, where someone on your team edits and sends them.

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}}'

Keys can cover the whole organisation, one pod of inboxes or a single inbox, so the support agent can't read the finance agent's mail.

Bring old mail with you

ACK imports an mbox file, a zip of .eml files, or pulls from an IMAP server. Imported mail is threaded like new mail and fires no webhooks, so your agent doesn't answer last year's email. There's also retention, legal hold and a full export of raw .eml files. The developers page lists every endpoint.

AgentMail vs ACK: side by side

AgentMail figures are from their pricing page and docs. ACK figures are from /pricing, /developers and /privacy.

Which should you pick?

Pick AgentMail if you want to start without a card, you want SDKs or calendar tools, or you need a SOC 2 report now.

Pick ACK if you want one price that covers every feature, you run more than a handful of inboxes and don't want to watch an email meter, or you need mail stored in the EU without an Enterprise contract. If you're running an agent per customer, the agents page shows how pods and scoped keys keep each one to its own mail.

FAQ

How do I move to ACK?

Create an organisation and inboxes, then point your code at ACK's REST API or your agent at its MCP server. How to give an AI agent its own email address walks through the main calls with curl, and you can import existing mail from mbox, a zip of .eml files or IMAP.

Does ACK have a free plan?

No. There's a 14-day trial. A card is needed to start, and you aren't charged until the trial ends. Trial inboxes use a shared ACK address and can send 100 emails in total. Receiving is unlimited.

Can I use my own domain on ACK?

Yes, on the paid plan. ACK gives you the DKIM, return-path and DMARC records to add. If you already have email on that domain, you can make it send-only and your current provider keeps receiving.

Does ACK work over MCP?

Yes. Point your client at https://mcp.ack.now/mcp with your key in an x-api-key or Authorization header. Add an email MCP server to your agent has the config.

How does ACK tell me about new mail?

With signed webhooks, at organisation, pod or inbox scope. How to receive email with webhooks covers signatures and retries.

Try ACK

Start the 14-day trial, create an inbox, and point your agent at it. If you want to compare properly, run the same job on both and see which one fits. Start a trial.