Opt-in
The user actively agrees to receive email, typically by submitting a signup form or checking a consent box.
Opt-in is the user's active agreement to receive email, typically by submitting a signup form, checking a consent box, or otherwise affirmatively indicating they want your messages. Opt-in is the opposite of opt-out (where the user is presumed to consent unless they actively decline).
GDPR, CASL, and most modern data-protection regimes require opt-in for marketing email — pre-checked boxes, bundled consent, and inferred consent from inaction are all invalid. US law (CAN-SPAM) is weaker; opt-out is technically permissible, but international senders typically default to opt-in to ensure global compliance.
Single opt-in adds the subscriber immediately on form submit. Double (confirmed) opt-in requires a confirmation email click before adding. Double opt-in is the gold standard for list hygiene and consent documentation but costs ~10–25% of completed signups.