Truelist

Email verification and deliverability validation. Validates single emails synchronously or bulk lists asynchronously. Returns an email_state + email_sub_state plus rich metadata (domain, MX record, suggested correction, disposable/role classification).

Spec source: Truelist-Labs/truelist-openapi (OpenAPI 3.1).

Capabilities

Authentication

• Type: Bearer token (API key)
• Header: Authorization: Bearer YOUR_API_KEY
• Get key: https://truelist.io/settings/api-keys
• Base URL: https://api.truelist.io

Common Agent Operations

Verify a single email (synchronous)

POST https://api.truelist.io/api/v1/[email protected]
Authorization: Bearer YOUR_API_KEY

No request body — the email is a query parameter. Returns a single-element emails array with verification fields:

{
  "emails": [
    {
      "address": "[email protected]",
      "domain": "example.com",
      "canonical": "[email protected]",
      "mx_record": null,
      "first_name": null,
      "last_name": null,
      "email_state": "ok",
      "email_sub_state": "email_ok",
      "verified_at": "2026-02-21T10:39:12.570Z",
      "did_you_mean": null
    }
  ]
}

Bulk verification (asynchronous)

POST https://api.truelist.io/api/v1/verify
Authorization: Bearer YOUR_API_KEY
Content-Type: application/json

{
  "emails": [
    "[email protected]",
    "[email protected]"
  ]
}

Processes the list in the background. The response acknowledges submission; results are available via the dashboard, the Truelist UI's CSV download, or via integrations (Mailchimp, Klaviyo, HubSpot, Zapier, Make, n8n, etc.).

For large lists, the dashboard's CSV upload + download flow is typically the lowest-friction path.

Get account information

GET https://api.truelist.io/me
Authorization: Bearer YOUR_API_KEY

Returns email, name, UUID, time zone, admin role, API keys, and account plan info.

Response Fields (per email)

email_state values

email_sub_state values

Pair the two: email_state: ok + email_sub_state: is_role means "deliverable but a role inbox," whereas email_state: email_invalid + email_sub_state: failed_smtp_check means "doesn't exist."

Rate Limits

A 429 is returned on rate-limit exceed. Note: the per-email validation rate is separate and depends on your plan.

Error Responses

All error bodies follow {"error": "<human-readable message>"}.

When to Use

• Before adding contacts to any cold outreach list — non-negotiable safety step. Apollo/ZoomInfo/Hunter data accuracy is typically 60–80%; Truelist catches the rest.
• Real-time form validation — block disposable / typo'd emails at signup. Use the inline endpoint (or the form validation widget).
• Periodic list hygiene — re-verify your active list quarterly to remove bounces before they hurt sender reputation.
• Pre-import validation on email platform imports (Mailchimp, Klaviyo, HubSpot, etc.) — direct integrations exist for most.
• AI agent workflows via the official MCP server for Claude, Cursor, and VS Code.

Why This Step is Non-Negotiable

Cold email reputation is built over months and destroyed in days. ISPs (Gmail, Outlook, etc.) track sender reputation through:

• Bounce rate — bounces over 2% trigger throttling
• Spam complaints — spam traps in unvalidated lists generate complaints
• Engagement — sending to dead mailboxes hurts engagement metrics

A single unvalidated send to a bought or scraped list can damage a domain's sending reputation for months.

Workflow Integration

Typical prospecting flow:

1. Build initial prospect list (Apollo, Clay, ZoomInfo, Hunter, GitHub stargazers, etc.)
2. For agent-driven workflows: use the Truelist MCP server to validate inline as the agent builds the list
3. For programmatic workflows: POST emails to /api/v1/verify for async bulk OR /api/v1/verify_inline for sync single
4. For one-offs: CSV upload via dashboard, download annotated CSV
5. Filter: keep email_state: ok, include risky/accept_all cautiously with a strategy, exclude email_invalid, re-verify unknown
6. Hand cleaned list to outreach platform (Instantly, Lemlist, Outreach, etc.) — see outreach.md, instantly.md, lemlist.md

Native Integrations (no API code required)

For non-developer workflows, Truelist has direct integrations:

• Email platforms: Mailchimp, Klaviyo, HubSpot, ActiveCampaign, Brevo, Constant Contact, ConvertKit, Drip
• Automation: Zapier, Make.com, n8n
• CRM / sales: Salesforce, Go High Level, Clay.com
• Ecom: BigCommerce
• AI / agents: MCP server (Claude, Cursor, VS Code)

See https://truelist.io/integrations for the current list.

Relevant Skills

• prospecting (primary use case — validate before adding to outreach lists)
• cold-email (downstream outreach against the validated list)
• emails (transactional senders + subscriber list hygiene)
• popups (real-time form validation on opt-in capture)