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How to connect mailfloss to Claude

Connect Claude Web, Desktop and Cowork to mailfloss MCP. Verify a single customer email address, check a batch of imported contacts, and more using natural language, with authentication handled for you.

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mailfloss is an email verification service with APIs for checking addresses and processing verification batches. It helps teams reduce invalid contacts and keep email lists clean.

12 Tools

Introduction

Claude is Anthropic's AI assistant, available on the web, in the desktop app, and on mobile. Cowork is its agent for knowledge work, and it runs on all of those surfaces too. Connected to your apps, Claude can work with your files and services to accomplish complex tasks on your behalf.

This guide walks you through the easiest and most secure way to connect your mailfloss account to Claude via Composio Connect, enabling it to verify a single customer email address, check a batch of imported contacts, track asynchronous email verification results, and more such actions on your behalf without compromising your account security.

Setup is the same on Claude Web, Desktop, and Cowork, and you only need to do it once. The connector is tied to your account, so it's available in all three.

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Connecting mailfloss to Claude Web, Desktop, and Cowork

Two ways to add the Composio connector. Pick whichever you prefer.

1. Add with one click

Click the button. Claude opens with the Composio connector filled in. Click Add, then go to step 2.

Add to Claude

Add manually

In Claude Desktop, click Customize in the left sidebar, then select Connectors and click the + icon at the top.

Claude Desktop connectors screen with Add custom connector selected

Click Add custom connector and paste in the Composio MCP server URL:

bash
https://connect.composio.dev/mcp
Add custom connector dialog with Composio MCP server URL

2. Authorize in your browser

Click Connect. You'll be redirected to a browser window where you can authorize Composio to continue.

Composio authorization screen for Claude Web, Desktop, and Cowork

3. Connect your mailfloss account

Back in Claude, ask it to connect to mailfloss or give it any mailfloss-related task.

For example, ask Claude to:

  • "Verify a single customer email address"
  • "Check a batch of imported contacts"
  • "Track asynchronous email verification results"

It will prompt you to authenticate and authorize access.

That's it. Composio's tools are now available in Claude, and your mailfloss account is ready to use.

What is the mailfloss Claude Connector, and what's possible with it?

The mailfloss MCP server is an implementation of the Model Context Protocol that connects your AI agent and assistants like Claude, Cursor, etc directly to your mailfloss account. It provides structured and secure access to email verification, batch processing, account details, and usage information, so your agent can verify email addresses, process verification batches, track job status and results, and manage stored verification records on your behalf.

  • Individual email verification: Have your agent check an email address and return its Mailfloss verification verdict.
  • Batch verification workflows: Direct your agent to submit groups of email addresses for verification, monitor processing status, retrieve results, or cancel pending jobs.
  • Verification history: Let the agent review past verification jobs, inspect their verdict breakdowns, and filter job history by source or lifecycle status.
  • Account and usage insights: Instruct your agent to check the connected API key, view account and organization details, and review verification usage for a selected period.
  • Record management: Have your agent permanently erase stored verification records for specified email addresses when they are no longer needed.

Troubleshooting

1. Why does Claude not use the Composio connector for mailfloss?

The connector can show as connected, but Claude must use it in each mailfloss conversation.

  • Click + at the lower left of the chat, or type /.
  • Hover Connectors.
  • Turn on Composio.
  • Ask Claude to connect to mailfloss again.

2. Why does Claude show an MCP server error before mailfloss connects?

Claude can show Couldn't reach the MCP server or Authorization with the MCP server failed when you add the connector for mailfloss.

  • Check that the connector URL is https://connect.composio.dev/mcp.
  • Connectors run from Anthropic's cloud, so your device network is usually not the problem.
  • Add the connector again from Customize > Connectors, then ask Claude to connect mailfloss.
  • If it fails again, send the error and the ofid_ reference id to support@composio.dev.

3. Why does the mailfloss authorization link not work?

The Composio connector is one server. Your mailfloss account connects separately when Claude asks for it.

  • If the browser does not open, or the link expires, ask Claude to retry the mailfloss connection.
  • Composio creates a fresh mailfloss authorization link.
  • Open that link in your browser and finish the mailfloss sign-in.

4. Why do mailfloss actions fail after they worked before?

The mailfloss connection can expire or lose permission.

  • Ask Claude to inspect the mailfloss connection.
  • If the connection is unhealthy, disconnect it when Claude prompts you.
  • Reconnect the mailfloss account and retry the action.
  • If Claude shows a permission prompt, approve it before Claude changes data in mailfloss.
  • If the action still fails with a permission error, check that the connected account has that permission in mailfloss itself.

5. How do I switch to a different mailfloss account?

Claude can manage the mailfloss connection for you.

  • Ask Claude to disconnect or delete the current mailfloss account.
  • Ask Claude to connect mailfloss again.
  • Open the new Composio authorization link for mailfloss.
  • Sign in with the other mailfloss account in the browser.
  • After the account connects, ask Claude to retry the mailfloss task.

6. Why is my mailfloss connection missing in Claude Desktop or on a Team plan?

The connector belongs to your Claude account, so your mailfloss connection works in Claude Web, Desktop, and Cowork.

  • In Claude Desktop, open Customize > Connectors.
  • Next to Composio, click ⋮ and click Clear cache.
  • If mailfloss tools still do not appear, click ⋮, disconnect, remove the connector, and add it again.
  • On Team or Enterprise, an Owner or Primary Owner must enable the connector before you can connect mailfloss.
TOOLS

Supported Tools

Every mailfloss action and event your agent gets out of the box.

Cancel Batch Verification

Cancel a pending or in-progress batch verification job.

Check API Key

Verify that the connected Mailfloss API key is valid.

Create Batch Verification

Submit email addresses for asynchronous batch verification and return the job ID.

Erase Verification Records

Permanently erase stored verification records for the supplied email addresses.

Get Account

Return the authenticated Mailfloss account holder's identity, contact details, security posture, notification preferences, and signup time.

Get Batch Verification Results

Return one cursor-controlled page of stored batch results after organization floss-setting overrides.

Get Batch Verification Status

Read an asynchronous batch verification job's state and available counters.

Get Verification Job

Return one verification job and its complete verdict breakdown.

Get Organization

Return the authenticated Mailfloss organization's plan, credit balances, current-period usage, trial state, account status, and feature entitlements.

Get Usage Report

Return verification usage for a UTC calendar period, optionally scoped to one ESP connection.

List Verification Jobs

Return one page of the organization's verification-job history, newest first, with optional source and lifecycle filters.

Verify Email

Verify one email address and return Mailfloss's raw engine verdict without organization floss-setting overrides.

FRAMEWORKS

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Atomic Agent

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FAQ

Frequently asked questions

With a standalone mailfloss MCP server, the agents and LLMs can only access a fixed set of mailfloss tools tied to that server. However, with the Composio Tool Router, agents can dynamically load tools from mailfloss and many other apps based on the task at hand, all through a single MCP endpoint.

Yes, you can. Claude Cowork fully supports MCP integration. You get structured tool calling, message history handling, and model orchestration while Tool Router takes care of discovering and serving the right mailfloss tools.

Yes, absolutely. You can configure which mailfloss scopes and actions are allowed when connecting your account to Composio. You can also bring your own OAuth credentials or API configuration so you keep full control over what the agent can do.

All sensitive data such as tokens, keys, and configuration is fully encrypted at rest and in transit. Composio is SOC 2 Type 2 compliant and follows strict security practices so your mailfloss data and credentials are handled as safely as possible.

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