Connecting MAILsimple to Claude

MAILsimple lets Claude work with your mailboxes. Setup takes a few minutes. Do these in order.

1. Subscribe

From Shop, choose a MAILsimple plan (there is a Free plan) and complete signup. Your subscription appears on your dashboard.

2. Add a mailbox

Go to mailsimple-mcp.ccmssolutions.com, sign in, and connect each IMAP or Outlook account Claude may use. Claude can only see mailboxes you add there, so do this before you connect. Sign in with the same email address as this CCMS account, and verify that address first (see the link we emailed you when you signed up; you can resend it from your dashboard) - otherwise the two can’t be linked.

3. Get your connection key

Open Connections and click Show connection key on the MAILsimple card. (If a key was already created with your subscription the button reads Reset connection key instead - click that; it gives you a fresh key to copy.) The key starts with csk_ and is shown only once. If you lose it, reset it again; the old key stops working.

4. Connect with the Claude Code plugin

In Claude Code, add the marketplace and install the plugin:

/plugin marketplace add ccms-inc/mailsimple-marketplace
/plugin install mailsimple-connector@ccms-hosting

Then give the plugin its two settings as environment variables, in the environment Claude Code runs in:

• MAILSIMPLE_MCP_URL = https://mailsimple-mcp.ccmssolutions.com/mcp (HTTPS, and it must end in /mcp)
• MAILSIMPLE_CONNECTOR_KEY = your csk_… connection key

# macOS / Linux (add to your shell profile)
export MAILSIMPLE_MCP_URL="https://mailsimple-mcp.ccmssolutions.com/mcp"
export MAILSIMPLE_CONNECTOR_KEY="csk_your-key-here"

# Windows PowerShell
setx MAILSIMPLE_MCP_URL "https://mailsimple-mcp.ccmssolutions.com/mcp"
setx MAILSIMPLE_CONNECTOR_KEY "csk_your-key-here"

Restart Claude Code so it picks up the values, then ask: “List my mail accounts.” Claude should return the mailboxes you added in step 2.

Other MCP clients

Any MCP client that can send an Authorization: Bearer header can connect: use the URL above and the header Authorization: Bearer csk_…. The custom-connector screen in claude.ai and Claude Desktop expects a sign-in flow rather than a pasted key, and one-click sign-in for CCMS connectors is not available yet, so use Claude Code or another client that supports headers for now.

Troubleshooting

An authentication error usually means the key is wrong or was reset: check it on Connections. A 404 means the URL is missing the /mcp path. A 402 or “subscription inactive” message means your subscription lapsed: settle it on Billing. If Claude connects but sees no mail, add a mailbox (step 2).