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Double Opt-In

GlossaryEmail intelligenceUpdated March 23, 2026

Definition
A two-step email subscription process where users confirm their signup by clicking a verification link sent to their email address.

Double opt-in is a subscription confirmation process that requires two steps before adding a person to an email list. First, the user submits their email address through a signup form. Then, they receive a confirmation email with a verification link that they must click to complete the subscription. Only after this second action is the email address added to the active mailing list.

This two-step process serves several important purposes. It verifies that the email address is valid and accessible, eliminates fake or mistyped entries, and confirms that the person genuinely wants to receive communications. As a result, double opt-in lists have significantly lower bounce rates, higher open rates, and better overall engagement compared to single opt-in lists. For organizations concerned about email deliverability and sender reputation, double opt-in is a powerful quality control mechanism.

While double opt-in is primarily used for marketing email lists, the underlying principle of email verification applies across all B2B outreach. Whether building a marketing list or a prospecting database, verifying email addresses before sending is always a best practice.

Key Points

  • Double opt-in requires users to confirm their subscription via a verification email
  • It produces higher-quality lists with better engagement rates and lower bounce rates
  • The verification principle applies to all email outreach, including B2B prospecting

Best Practices

  • Use double opt-in for all marketing email lists to protect sender reputation
  • Design confirmation emails that are clear and make it easy to complete the verification step
  • Monitor confirmation rates to identify issues with your signup flow or email delivery

Free Tools

// 02 · in practice with tomba

The API calls behind this term

Verify an address before it reaches a sequence, and find the right one when you only have a name and a company domain.

GET/email-verifier1 verification creditGET/email-finder1 search credit

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  1. 1Create a free account25 searches a month. No card.
  2. 2Copy your key and secretFrom API keys in the dashboard.
  3. 3Call the APIPaste the request; the answer is JSON.
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curl "https://api.tomba.io/v1/email-finder?domain=piedpiper.com&first_name=Richard&last_name=Hendricks" \
  -H "X-Tomba-Key: $TOMBA_API_KEY" \
  -H "X-Tomba-Secret: $TOMBA_SECRET_KEY"
Response
200 OK· 1 search credit
{
  "data": {
    "email": "richard@piedpiper.com",
    "first_name": "Richard",
    "last_name": "Hendricks",
    "full_name": "Richard Hendricks",
    "website_url": "piedpiper.com",
    "company": "Pied Piper",
    "pattern": "{first}",
    "department": "executive",
    "type": "personal",
    "position": "CEO",
    "country": "US",
    "gender": "male",
    "twitter": null,
    "linkedin": "https://www.linkedin.com/in/richard-hendricks",
    "score": 100,
    "accept_all": false,
    "phone_number": true,
    "verification": {
      "date": "2025-01-15T10:32:00+01:00",
      "status": "valid"
    },
    "sources": [
      {
        "uri": "https://piedpiper.com/blog/engineering",
        "website_url": "piedpiper.com",
        "extracted_on": "2024-06-01T09:14:07+01:00",
        "last_seen_on": "2025-01-10T17:02:44+01:00",
        "still_on_page": true
      }
    ],
    "phone_data": []
  }
}