I built MailboxKit because I kept running into the same problem: AI agents need email but existing APIs aren't designed for them.

The typical flow for an agent is: get an email address, send messages, receive replies, and handle threading — all via API, without a human setting things up. Most email services require manual domain verification, complex OAuth, or aren't built for programmatic access from the start.

MailboxKit lets an agent self-register and start sending/receiving in a single API call:

``` POST /api/v1/register {"name": "My Agent", "owner_email": "you@example.com"}

→ {"api_key": "mbk_...", "email": "abc123@agent.mailboxkit.com", "inbox_id": '19999d'} ```

That's it. The agent now has a real email address, can send and receive, and gets inbound messages via webhooks. Threading, read/unread tracking, attachments, and custom domains all work out of the box.

The API docs double as an LLM-readable skill file (mailboxkit.com/skill.md) so agents using tool-use can discover and learn the API themselves.

Currently used by a handful of agents doing customer support, research, and outreach. Would love feedback from anyone building agent infrastructure.