Lettermint

European Transactional Email

Documentation

Connect an AI client to Lettermint to inspect email activity and manage your email setup. Lettermint hosts the server, so you do not need to install a local process.

Codehttps://api.lettermint.co/mcp

Before you connect

You need:

A verified and active Lettermint account.
At least one team where MCP is enabled. MCP is on by default for every team.
An MCP client that supports remote Streamable HTTP servers and OAuth.

Use OAuth to connect. Project API tokens and Team API tokens do not work with the hosted MCP server.

Connect your client

Choose your client. Cursor users can also add Lettermint in one click.

The named clients below register an OAuth client automatically. You do not need to enter an OAuth client ID or client secret.

Open ChatGPT plugins, select +, and select Add custom MCP server. Enter these values:

CodeName: Lettermint
Server URL: https://api.lettermint.co/mcp
Authentication: OAuth

Confirm the warning, select Create as a plugin, and sign in to Lettermint. In a new chat, type @ and select Lettermint.

Custom MCP servers work in ChatGPT on the web. OpenAI decides which plans can add them and use write actions. In a Business or Enterprise workspace, an admin may need to allow you to create plugins with MCP servers.

Your client opens a browser. Sign in to Lettermint, review the connection, and approve access.

ChatGPT on the web does not load the MCP settings from your local Codex clients. Add Lettermint there as a custom MCP server.

Check the connection

Start with a read-only request:

Use Lettermint to list my teams and projects. Do not change anything.

The client should call list_teams first. This tool returns only the teams that you can access through MCP. It also returns the effective capabilities for each team.

What you can do

Lettermint provides focused tools for these areas:

Area	Capabilities
Documentation search	Find Lettermint product and API guidance.
Teams, roles, and members	List teams and effective capabilities. Inspect roles and members. Rename teams, update member assignments, invite or remove members, manage pending invites, and manage custom roles when allowed. List Team API tokens and change their abilities.
Projects and routes	List, create, update, and delete projects and routes. List Project API tokens and create new ones for API and SMTP sending.
Bounce and complaint forwarding	Set, verify, or remove the address that receives bounce and complaint reports for a project. See Bounce and complaint forwarding.
Domains and DNS	Manage domains and project associations. Check sending DNS and verify inbound domains.
Email activity, content, statistics, and usage	Search messages, inspect delivery events, read permitted message content, review delivery statistics, and check usage.
Deliverability analytics	Query rates, breakdowns, latency, and period comparisons on the Pro plan. See Ask an AI assistant about your analytics.
Sending and scheduled email	Send one message or a batch, or resend a sent message. Schedule, reschedule, or cancel messages.
Webhooks	Manage webhook endpoints, inspect deliveries, send tests, retry failed deliveries, and rotate signing secrets.
Suppressions	Search, add, and remove suppression entries.

Your MCP client loads current tool names and input schemas from the live catalogue. Use list_teams to see the actions that your role can use for each team.

How access works

The OAuth connection belongs to your user account, not to one team.
Every team-scoped request includes an explicit team_id. Every project-scoped request also includes an explicit project_id.
Lettermint checks your current membership, project access, role permissions, MFA requirements, and team settings on every call.
Disabling MCP for a team blocks new and existing connections from that team at once. It does not disconnect the user from other teams.
Reading message metadata and reading message content are separate permissions.
Message content follows the data retention policy.
MCP OAuth credentials work only with the hosted MCP server. They cannot call /v1 or /rest/v1.

See Roles and Project access for the permissions that Lettermint applies.

Personal-information filtering

Personal-information filtering is enabled by default for each team. The filter limits data that can identify a person and actions that can confirm an identity.

Area	Result while filtering is enabled
Message lists and details	Lettermint hides sender and recipient identities, recipient names, reply-to addresses, subjects, tags, metadata, attachment names, and media types. Delivery IDs, dates, status, and other operational fields remain available.
Message content	Message bodies and raw source are not available.
Identity searches	Free-text message searches and searches by suppression value are not available.
Deliverability analytics	Queries on the `from_address` and `subject` dimensions are not available.
Team members	Member lists, member details, invites, member removal, and member assignment changes are not available. Role definitions remain available.
Sending	Single and batch sending and resending are not available.
Suppressions	Values are hidden. New entries and searches by value are not available. Removal by suppression ID can still be available.
Configuration	Permitted team, project, route, domain, and webhook configuration remains available.

A member with Manage team security can change this setting with Filter PII under Applications in the team settings. The option appears while MCP is enabled.

If you turn off the filter, an MCP client can receive personal information and perform permitted identity-related actions. The normal role and project checks still apply.

Write actions and confirmations

MCP actions change live Lettermint data when your permissions and team settings allow them.

Lettermint rejects these actions unless the request includes confirm=true:
- Deleting projects, routes, domains, webhooks, and custom roles, removing members and suppressions, revoking invites, and canceling a scheduled email.
  - Sending a batch, sending one email to more than one recipient across to, cc, and bcc, and resending a sent message.
  - Inviting members, changing invites, roles, and member assignments, and changing which projects a domain belongs to.
  - Creating a Project API token, changing a Team API token's abilities, and rotating a webhook signing secret.
  - Suppressing a whole domain.
Your client should show you the details and ask for your approval before it sets confirm=true.
Removing a spam complaint suppression does not delete it. Lettermint opens a review ticket, and the suppression stays active until support approves the removal. See Remove suppressions.
Every email send requires an idempotency_key. See Idempotency.
Webhook creation returns the signing secret once. Secret rotation also returns the new secret once. Webhook read tools never return a signing secret.
Creating a Project API token returns the token once. The token passes through your MCP client and the AI model, so let the assistant write it straight into your configuration or secret store. You can revoke it in the dashboard, where it shows via MCP. Token lists never return token values.
When you change a Team API token's abilities, integrations that use the token lose removed abilities immediately. You can only grant abilities your role allows.
Your MCP client can require its own approval or block a write action before the request reaches Lettermint.

Use the Lettermint test address when you test sending:

Send one test email to ok@lettermint.dev. Use a new idempotency key. Show me the message details before you send it.

Messages to this address simulate a successful delivery. They do not reach a real inbox. See Test email addresses.

Example prompts

"List the Lettermint teams and projects I can access."
"Summarize delivery statistics for this project for the last seven days."
"Find failed messages from today and explain their delivery events."
"Check the DNS verification state for this sending domain."
"Create a project and add a route for its production traffic. Show me the planned changes first."
"Schedule an email for tomorrow at 09:00 Europe/Amsterdam. Show me the message and time before you send it."
"Create a webhook for failed and delivered events, then send a test event."
"Create a Project API token for production and put it in my app's Lettermint configuration."
"Search the Lettermint documentation for sending domains and DKIM."

Manage the connection

Open Account settings > Applications to review or revoke a connection. Revoking a connection invalidates its MCP access across all teams.

A member with Manage team security can open the team settings and use Enable MCP and Filter PII under Applications to turn MCP off or change personal-information filtering for a team.

Troubleshooting

Problem	What to check
OAuth registration failed before	Remove the failed Lettermint connector or server entry. Add it again with `https://api.lettermint.co/mcp`. Select automatic registration if the client gives you that choice.
Lettermint does not appear in Codex	Run `codex mcp list` or use `/mcp`. Confirm that the server is enabled and authenticated. Restart the desktop app or IDE after you add the server.
ChatGPT web does not show Lettermint	ChatGPT web does not load local Codex MCP settings. Add Lettermint as a custom MCP server in ChatGPT plugins, then type `@` in a new chat and select it.
The sign-in page is unavailable	Confirm that your account is active and verified. Confirm that Enable MCP is on for at least one team.
A team or project is missing	Check your membership, project assignment, MFA state, and the team's Enable MCP setting. A blocked or frozen team is not available through MCP.
A tool returns a permission error	Check your role. A new connection does not change your permissions.
Personal data or sending is unavailable	Check the team's Filter PII setting.
Sending is denied when filtering is off	Check sender verification, team status, quota, spend limits, and suppressions.
The client blocks a write action	Review the client's approval and safety settings. If the client blocks the action, Lettermint receives no tool call.
A webhook signing secret is missing	Lettermint returns the secret only after creation or rotation. Rotate the secret if you did not store it.
An OAuth token cannot call `/v1` or `/rest/v1`	This is expected. MCP OAuth credentials work only with the hosted MCP server.