Double opt-in is a two-step signup confirmation. After someone submits a signup form, they are not added to your list immediately; instead they receive an email with a confirmation link, and only by clicking it do they confirm the subscription. The "double" refers to the two actions: filling the form, then confirming via email.
The practice exists to prove that the person who entered an address actually controls it and genuinely wants to subscribe. This filters out typos, fake addresses, and malicious signups using someone else's email, and it produces a cleaner, more engaged list with better deliverability. In some jurisdictions it also strengthens the record of consent.
The trade-off is a small drop in completed signups, since some people never click the confirmation - so it is most worthwhile for marketing lists where list quality and consent evidence matter. The forms guide covers autoresponders and confirmation flows that make this smooth.
Related terms
Autoresponder
An automatic confirmation email sent to the person who submitted a form, acknowledging receipt and setting expectations.
GDPR-compliant form
A form whose data collection, storage, retention, and deletion meet the requirements of the EU General Data Protection Regulation.
Spam filtering
The layered techniques a form backend uses to keep automated and unwanted submissions out of your inbox without blocking real people.
Read the full guide