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Email validation for AI agents

Published 2026-10-17

Agents that read inboxes, fill CRMs or book meetings pick up contact data from messy places: email signatures, web pages, chat transcripts. A mistyped domain or a throwaway inbox that gets saved means a bounced follow-up later, and the agent never notices. ContactLint gives the agent a tool to check first.

Connect it

ContactLint runs a hosted MCP server at https://contactlint.com/mcp (streamable HTTP, JSON-RPC 2.0). There is nothing to install. Add it to any client that supports remote servers:

{
  "mcpServers": {
    "contactlint": {
      "type": "http",
      "url": "https://contactlint.com/mcp",
      "headers": { "Authorization": "Bearer YOUR_KEY" }
    }
  }
}

It is also listed in the official MCP Registry as com.contactlint/contactlint. initialize and tools/list work without a key, so you can inspect the tools before you sign up.

The three tools

Tool	Arguments	Returns
validate_email	`email`	verdict (valid, risky, invalid, unknown), reason, did_you_mean, disposable, role_address, free_provider, MX records
validate_emails	`emails`: up to 50	one result per address in order, plus a summary of verdicts
validate_phone	`phone`, optional `country`	valid, possible, type, region, E.164, national and international formats

Tell the agent what to do with the result

Add a short rule to your system prompt or agent instructions:

Before you save or email a contact, call validate_email.
- verdict "invalid": do not save it; tell the user the address cannot receive mail.
- did_you_mean is set: ask the user whether they meant that address.
- reason "disposable": do not add it to the CRM.
- reason "role_address": save it, but do not treat it as a person.
- verdict "unknown": save it and note that it could not be checked.

What it costs

Each address or number checked uses one check: 100 free per key each month, then credit packs from $9 for 5,000. A validate_emails call with 50 addresses uses 50 checks and counts as one request toward the 60 requests per minute limit. If the key does not have enough checks for the whole list, nothing is checked or billed and the tool returns an error that starts with quota_exceeded. Checks whose DNS lookup fails come back with reason dns_error and are not billed.

What it does not do

It does not connect to mail servers, so it cannot confirm that a mailbox exists or detect catch-all domains. It does not look up phone carriers. For the full setup per client and error codes, see the email validation MCP server guide.

Questions

Which MCP clients work with ContactLint?

Any client that supports remote MCP servers over streamable HTTP and lets you set an Authorization header. Clients that only run local stdio servers need a bridge.

Does the agent need a separate key?

It can share your key, but a separate key per agent makes usage easier to track. Create keys free at contactlint.com/signup.

Can the agent clean a whole list?

Yes. validate_emails takes up to 50 addresses per call. For bigger lists, call it in chunks or use the REST batch endpoint.

Get a free API key. 100 checks per month, no card required. Or try a live check first.