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Set-up documentation
Connect your mailbox to Cline
Cline spells the transport streamableHttp in camel case, alone among every client. OAuth is not in its documentation, so this one takes an access token.
mcpServers
url
This one takes an access token
Most clients in this section need nothing but a URL, because they sign you in. Cline is one of the ones that does not, and the reason is worth stating precisely rather than as a verdict: OAuth is not mentioned anywhere in Cline's own MCP documentation. Three of its pages were read on 30 August 2026 and all three describe API keys, tokens and custom headers only.
That is a gap in the documentation rather than a documented refusal, so it is possible Cline handles a sign-in and simply has not written it down. The token route is what we can tell you works. Create one in the control panel for the mailbox you want Cline to reach.
A token is a credential, so treat it like one
It opens one mailbox until you revoke it. Do not commit the file it lives in, do not paste it into a chat window, and revoke it in the control panel the moment you stop using it. Every client that signs in instead is one fewer of these in existence, which is the whole argument for the OAuth route where a client offers it.
The configuration
{
"mcpServers": {
"work-mail": {
"type": "streamableHttp",
"url": "https://mcp.mailbox-mcp.com/db/mcp/YOUR-MAILBOX-KEY",
"headers": {
"Authorization": "Bearer YOUR-ACCESS-TOKEN"
},
"disabled": false,
"autoApprove": []
}
}
}
streamableHttp is camel case and Cline is alone in spelling it
that way. Its documentation says to set this explicitly for the recommended
transport, and to use "type": "sse" only for legacy SSE
servers, which this is not.
autoApprove is worth a thought rather than a copy. An empty
list means Cline asks before every call, which on a mailbox is the right
default. If you do put tool names in it, put read tools there and nothing
else: an auto-approved send_email is an agent that can send
mail in your name without asking, and every auto-approved read still counts
against your daily call limit.
Or add it through the panel
The same thing without editing a file: the MCP Servers icon, then the Remote Servers tab. It asks for a server name, a server URL, and a transport type, where the choices are Streamable HTTP (recommended) and SSE (Legacy). Pick the first. Then Add Server.
Which file
~/.cline/mcp.json is the only path in Cline's own
documentation, and it is the CLI's. The VS Code extension keeps its
settings somewhere under the editor's global storage, and that path is not
vendor-documented anywhere we could find, so it is in the unconfirmed list
at the foot of this page rather than printed here as though it were
certain. If you use the extension, the panel route above avoids the
question entirely.
Check that it worked
Try this first
Read my three most recent unread emails and tell me if any of them are about something in this codebase.
Nothing is marked read by asking. A 401 rather than a result means the token, not the URL: check you pasted the whole of it and that it has not been revoked.
The free tier is 5 MCP calls a day on any mailbox, with no card. Enough to try Cline against your own mail before deciding.
Where to go next
If you also use VS Code's own agent mode, that one does sign you in and needs no token at all, which is the better arrangement where you have the choice. The key table shows which clients are which.
- The IDE extension's settings path. Only the CLI path is in vendor documentation; the cline_mcp_settings.json location under globalStorage comes from third parties.
- Whether Cline supports OAuth at all. It is not mentioned on any of three vendor pages read, which is why this page uses a token.
Read 30 August 2026 Every value on this page came off Cline documentation: MCP overview on that day. If it has changed since, tell us and we will read it again.