Codex stores MCP settings in the config.toml file, and the CLI, the IDE extension and the desktop app all use the same file — you only need to configure it once. The global file is located at ~/.codex/config.toml; a per-project configuration can be placed in .codex/config.toml, but it is picked up only in a trusted project.

Option 1 — via the CLI (recommended)

  1. Add the server:
codex mcp add emailmassivo --url https://mcp.emailmassivo.com/mcp

  1. Check that it was saved: codex mcp list (details for a specific server — codex mcp get emailmassivo).

  2. Authorize:

codex mcp login emailmassivo

  1. The browser opens with the Email Massivo authorization page — log in to your account and click "Allow".

  2. Run codex and execute /mcp — Email Massivo should appear in the list of active servers.

If codex mcp login fails or Codex crashes on startup with the error missing field command in mcp_servers.emailmassivo, your Codex version is outdated and does not support remote servers directly. Update Codex — in current versions streamable HTTP works out of the box. As a temporary workaround, add the following block at the beginning of ~/.codex/config.toml: [features] experimental_use_rmcp_client = true

Option 2 — editing config.toml

Add a block to the ~/.codex/config.toml file (on macOS and Linux — ~/.codex/config.toml, on Windows — %USERPROFILE%\.codex\config.toml, i.e. C:\Users\<username>\.codex\config.toml). If the file does not exist yet, create it.

[mcp_servers.emailmassivo]
url = "https://mcp.emailmassivo.com/mcp"

Then run codex mcp login emailmassivo and complete the authorization.

Option 3 — via the ChatGPT desktop app settings

The separate "Codex Desktop" app has been discontinued: the same functionality (MCP, plugins, hooks, Git, worktrees) is now built into the ChatGPT desktop app — it is located in its settings, in the "Integrations" and "Code" sections. This current path is described below.

  1. Open the ChatGPT app settings and in the "Integrations" section select "Plugins".

  2. On the "Plugins" page, switch to the "MCP" tab (the counter next to it shows how many servers are already connected — do not confuse it with the "Plugins", "Skills" and "Store" tabs).

  3. Click "Add" → in the dropdown menu select "Add MCP server" (not "Create plugin" and not "Add marketplace").


ChatGPT settings: "Plugins" (1) → "Add" (2) → "Add MCP server" (3); in the form — "Name" (4), "Type" (5), "URL" (6), "Save" (7)

  1. In the "Name" field, enter Email Massivo.

  2. In the "Type" field, select "Streamable HTTP" (not STDIO).

  3. In the "URL" field, paste:

https://mcp.emailmassivo.com/mcp

  1. Leave the "Bearer token environment variable" and "Headers" fields empty — Email Massivo authorizes via OAuth, not via a static token.

  2. Click "Save".

  3. An "email_massivo" row appears in the list on the MCP tab with an "Authenticate" button on the right (next to it — a settings icon and the server enable toggle).


The email_massivo row in the MCP list: "Authenticate" button, settings icon and server enable toggle

  1. Click "Authenticate" — the browser opens with the Email Massivo authorization page. Log in to your account and click "Allow".


Email Massivo authorization page — "Allow" button