Double Opt-in
A signup method that requires a subscriber to click a confirmation link in an email before they are added to your list.
Double opt-in (also called confirmed opt-in) adds a confirmation step to signup: after someone submits a form, they receive an email with a link and join your list only once they click it. That proves the address is real, belongs to the person who signed up and can receive your mail, which keeps typos, bots and spam-trap addresses off your list. The trade-off is that some people never confirm, so the list grows more slowly.
Is double opt-in required?
In the US, CAN-SPAM does not require any opt-in for commercial email; it requires a working opt-out. In the EU, the GDPR says a business relying on consent must be able to demonstrate it (Article 7), and double opt-in is a common way to keep that proof: a timestamped confirmation click. The regulation does not name double opt-in, and national rules and regulators' expectations vary, so get legal advice if you mail EU subscribers.
To set it up, turn it on in your platform's form or list settings, customize the confirmation email, and send new subscribers to a page telling them to check their inbox.
What to put in the confirmation email
Name your brand in the From line and subject, say in one sentence what the person signed up for, and make the confirm button the only call to action. If you promised a download or discount, deliver it after the click so people have a reason to confirm.
Common double opt-in mistakes
A generic confirmation subject line that people ignore or that lands in spam. No reminder for people who have not confirmed. Using double opt-in on forms but bulk-importing unconfirmed contacts anyway. Some signups will never confirm, so track the confirmation rate in your platform and rewrite the email if it is low.