Built for agents as well as people.
Courier's web client is one client of its API. An agent is another: it can read, search, draft, send, schedule, file, and run rules, all as tools.
148 tools, one rule
Every MCP tool is a thin adapter over a REST route, so an agent and a person always see the same data and follow the same checks. Tests compare the tool list against the routes and fail when either side drifts.
The tools fall into thirteen groups: messages and threads (24), AI and search intelligence (20), outreach controls (20), contacts (13), compose and send (12), labels and folders (12), signatures and identities (11), search and smart folders (8), accounts (7), rules (7), block and allow lists (6), service and settings (4), and push (4).
AI features on the server
Courier computes embeddings for your mail on the server and uses them for semantic search that blends meaning with full-text matching. On top of that it can summarize a thread, a contact, or a topic, track commitments you made and replies you are owed, draft a reply, prepare a briefing before a meeting, link related threads, collect facts into a knowledge base, tag the tone of messages, and suggest rules.
A fast model handles most of it. Contact and topic summaries and the optional Sonnet reply drafts use a Claude model. Every feature needs a model key. Without one, it reports that it is not configured and does nothing; it never fails a request or a background job.
A monthly budget applies to each account, with a hard stop when it is spent. These features answer through the API and the agent tools.
Outreach for other tools
Courier lets other Renkara tools send outreach through a person's account without giving up control. A tool creates a draft; Courier returns a proof of the exact content; a person approves that exact version; and only then is it dispatched. Failures can be retried with a fresh approval, and delivery, bounce, and reply outcomes come back in one normalized form.
A suppression list stops mail to people who opted out, and signed intake accepts complaint and unsubscribe notices from the sending tool.
Mail stays behind the API
Whether the caller is the web client, an agent, or a native app, it reads and writes Courier's database through the same REST routes, and only the server talks to Gmail, Microsoft 365, or an IMAP server.
Questions about this tool?
Write to Renkara Media Group and a person will answer.