Blog
How ACK works, how to build with it, and what changed.
Email for AI agents: what an agent needs and how to give it one
What an AI agent needs from email, how Gmail, sending APIs and agent inbox services compare, and how ACK handles each part.
Read the postEarlier posts
· 7 min
AgentMail alternative: how ACK compares
What AgentMail does well, where ACK differs on pricing, drafts and EU hosting, and a side-by-side table sourced from both sites.
7 min
· 7 min
What is an email thread, and how does threading work?
An email thread is a message and its replies. Here's how Message-ID, In-Reply-To and References hold it together, and why threads break.
7 min
· 7 min
Resend pricing explained, and when your agent needs an inbox
Resend's plans, quotas and overage rates as of 27 October 2026, plus how inbox pricing and draft-only keys compare with ACK.
7 min
· 6 min
Resend API: send and receive email, with code from the docs
Send email with the Resend API, receive it by webhook, reply in thread, and how Resend Inboxes compare with ACK for agent email.
6 min
· 6 min
Resend MCP: what it does, and when your agent needs its own inbox
What Resend's MCP server covers and how to install it, and how an agent-owned inbox over MCP keeps each agent to its own mail and drafts.
6 min
· 6 min
Resend vs SendGrid vs Postmark: pricing, free tiers and inbound email
Resend, SendGrid and Postmark compared on free tiers, paid plans, receiving mail and developer tools, with every number from the vendors' own pages.
6 min
· 2 min
How to give an AI agent its own email address
Create an inbox, get told when mail arrives and reply in the same thread. Each step comes with the request to copy.
2 min
· 2 min
Approve your agent's email before it goes out
Give the agent a key that can write drafts but can't send them. A person reads each draft in the app and clicks Send.
2 min
· 3 min
How to receive email with webhooks
Register an endpoint, check the signature on every delivery, and know what ACK does when your server is down.
3 min
· 2 min
Add an email MCP server to your agent
One URL and one API key give your agent 39 tools for reading, sending and drafting mail. The key decides which inboxes it can touch.
2 min
Give your agent an inbox today.
Sign up, create an inbox and send your first email in a few minutes.