Words used here

Short definitions for the terms these pages use, in case any of them are new.

Documentation for email infrastructure tends to assume you already speak it. This page is here so the rest of these pages can be read without that being true. Nothing below is something you have to configure.

Agent: Whatever is doing the work: an assistant you run, a script you wrote, a workflow in n8n. On these pages it also means the identity that work uses, which is one handle and one mailbox.
Handle: The short name an agent goes by, like scout. It is the part before the @ in its address, and it is unique across all of MCPmailer rather than just inside your account.
Mailbox: One agent's email: the address it sends from, and where its mail arrives. An agent has exactly one and cannot read anyone else's.
Workspace: Your account and everything in it: the agents, the shared address book, the notes, the vault, and the plan you are on.
MCP: The Model Context Protocol, a standard way for an assistant to pick up tools from an outside service. Connecting over MCP is what makes sending and reading email appear as things your assistant can do. You do not need to understand it to use it.
API key: A long secret starting with mmk_ that stands in for one agent. Anything holding it can send as that agent, so it belongs in a settings field or an environment variable, never in a message or a prompt.
Signing in instead: Some apps can send you to a page here to approve them, so no key is ever copied anywhere. Where it is offered it is the shorter route, and you can revoke that one app later without touching the others.
Thread: One conversation: a message and every reply under it. Answering with reply_all keeps a thread together the way a person's mail client does.
Reply and cold send: A reply answers someone who wrote to you first. A cold send is a first contact, and is treated more carefully: it carries an unsubscribe link and is watched for runaway sending.
Webhook: A message we send to your software the moment something happens, instead of your software asking us over and over whether anything has. It is how mail can wake an agent that is already running.
Suppressed address: An address that bounced or reported one of your messages as spam. We refuse later sends to it, because writing to it anyway is what gets a sending domain blocked.
DNS records: Settings on a domain you own. Publishing ours proves the domain is yours and lets the receiving side trust mail your agents send from it.
Disposable address: A throwaway address that receives for a short while and is then deleted along with everything it received. For signups and verification codes.
Tunnel: A public web address that points at something running on your own machine, so an outside service can reach it even from behind a home network.
The vault: Where credentials an agent needs are kept, encrypted, so it can use one without anybody pasting it into a conversation.