What is double opt-in?

Double opt-in (DOI), sometimes called "confirmed opt-in", is a subscriber-acquisition pattern where users who submit a signup form do not get added to the list immediately. Instead, they receive a confirmation email with a link they must click. Only after clicking are they added to the active list.

Benefits:

• Confirms ownership of the email address.
• Filters out typos automatically. john@gmial.com will not receive the confirmation.
• Filters out disposable services (the confirmation arrives at a throwaway inbox the user no longer checks).
• Provides court-defensible proof of consent, required under strict GDPR interpretations in some EU jurisdictions.
• Higher engagement on the resulting list (subscribers who confirmed care enough to click).

Costs:

• 20 to 40% drop-off in signups (some users never click the confirmation).
• Confirmation emails sometimes land in spam, permanently losing that user.
• Adds friction to the signup funnel.

A middle path: single opt-in with real-time verification on the form catches typos and disposables at entry without requiring the confirmation click. See should I use double or single opt-in.