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Connect Fastmail to Claude

Connect Fastmail to Claude through Fluxmail with an app password. Search mail, read attachments, and draft replies across one or more Fastmail accounts.

Richard Chu

Fluxmail Founder

4 min read

A paper envelope flying forward on one folded wing with a glowing edge

Fluxmail connects Fastmail to Claude over IMAP and SMTP, the protocols desktop mail apps use, with an app password. Claude can search and read your mail, open attachments such as PDF invoices, move messages between folders, and write drafts that show up in Fastmail on the web and on your phone.

One Fluxmail connection can include several Fastmail accounts, and Gmail, Outlook, or iCloud mailboxes next to them. Claude uses the same tools for all of them.

You can set it up two ways. Fluxmail Cloud is a hosted connector you add from Claude's connector directory, and it works in Claude Desktop, Claude on the web, Claude Code, and other MCP clients. Self-hosted Fluxmail runs on your computer, keeps the password encrypted there, and works with Claude Code and Claude Desktop. Both start with an app password.

1. Create a Fastmail app password

Fastmail's Basic plan doesn't include IMAP or app passwords, so you need one of its other plans.

  1. In Fastmail, go to Settings > Privacy & Security.
  2. Under Connected apps & API tokens, select Manage app passwords and access.
  3. Select New app password and confirm your password if Fastmail asks.
  4. Name it "Fluxmail" and keep the default access, Mail, Contacts & Calendars, which includes IMAP and SMTP.
  5. Select Generate password and copy it.

Fastmail shows the password once. To cut off Fluxmail later, disable or remove the password on the same page.

2. Connect with Fluxmail Cloud

  1. Sign up for Fluxmail Cloud. A new workspace gets a seven-day trial, and you don't need a card to start it.
  2. Open Mailboxes, choose Other email provider, and enter your Fastmail address. For @fastmail.com and @fastmail.fm addresses, the dashboard fills in Fastmail's servers.
  3. Paste the app password and select Connect.

If you use your own domain with Fastmail, enter the servers yourself: imap.fastmail.com on port 993 and smtp.fastmail.com on port 465. Repeat these steps for each Fastmail account you want Claude to reach.

Then add Fluxmail to Claude from the connector directory:

  1. In Claude, open Customize > Connectors and select Discover.
  2. Search for Fluxmail and select +.
  3. Sign in to Fluxmail and pick your Fastmail mailboxes. The connector requests Full mail access, which includes sending, so uncheck Send emails and anything else you don't want, then approve.

To use Cloud from Claude Code, Cursor, or another client, follow How to connect Gmail or Outlook to Claude, ChatGPT and Cursor. The commands are the same for Fastmail.

3. Or run Fluxmail on your computer

Skip this step if you connected through Fluxmail Cloud.

Install the Fluxmail CLI and create the local administrator:

npm install -g fluxmail
fluxmail setup --name "Your name" --email you@example.com

Then connect Fastmail with Fastmail's server settings:

fluxmail accounts add imap \
  --email you@fastmail.com \
  --imap-host imap.fastmail.com \
  --smtp-host smtp.fastmail.com \
  --smtp-port 465 \
  --smtp-security tls

Use your own address, including a custom domain if you have one. Fastmail uses the full address as the username, which is Fluxmail's default. Fluxmail asks for the password without showing it, tests both connections, and encrypts the password in its local database.

Add Fluxmail to Claude Code with read-only access while you try it out:

claude mcp add fluxmail -- fluxmail stdio --profile read-only

For Claude Desktop, open Settings > Developer > Edit Config and add this to claude_desktop_config.json, then restart Claude Desktop:

{
  "mcpServers": {
    "fluxmail": {
      "command": "fluxmail",
      "args": ["stdio", "--profile", "read-only"]
    }
  }
}

4. Try it

Ask for something that needs an attachment:

Find the invoices I received in Fastmail last month and list each vendor, amount and due date.

Claude finds the messages with search_emails and opens each PDF with download_attachment. Extract invoices from email attachments goes further and builds a spreadsheet from them.

5. Allow more when you need it

When you want Claude to file mail or write drafts, widen access. In Cloud, connect Claude again with the permissions you want and revoke the old connection in Connections. In self-hosted Fluxmail, switch the profile to read-write, or to full to allow sending. Over IMAP, Fluxmail moves messages between Fastmail folders and doesn't apply labels, so ask Claude to move messages rather than label them.

If something looks off

  • Fastmail rejects the login. Use the app password, not your Fastmail password, and check that it has mail access.
  • Sent messages appear twice. Fastmail can save its own copy of mail sent over SMTP. If you see duplicates in Sent, connect the mailbox again with Save sent mail to the Sent folder turned off in Cloud, or add --no-save-sent to the fluxmail accounts add imap command.
  • A folder is missing. Fluxmail finds Sent, Drafts, Trash, Archive, and Spam from the flags Fastmail reports and then by common names. If one isn't detected, set it under Folder mappings in Cloud, or with fluxmail accounts configure <account-id> in self-hosted Fluxmail.

Next steps

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