What is double opt-in and should you use it?
Double opt-in means a subscriber confirms their signup through an email link first. It is not legally required everywhere, but it is best practice: it proves consent, keeps fake addresses out, and keeps your list clean and deliverable.
With single opt-in, someone is on your list the moment they submit the form; with double opt-in they first receive a confirmation email with a link to click. Only after that click is the signup complete. You lose a few percent of signups (people who forget to confirm), and that is precisely the point: what remains are real, willing subscribers.
Legally, the confirmation click is your evidence of consent. Privacy rules like the GDPR for European readers demand demonstrable consent, and the timestamp plus IP address of the confirmation (every serious tool logs it automatically) is the gold standard. US rules under CAN-SPAM are looser, but if any of your readers are in Europe, the stricter standard is the safe one.
Practically, it also prevents misery: typos, pranksters entering someone else's address, and spam bots never make it through. That keeps your bounce rate low, which in turn protects your deliverability. Just switch it on; every tool in our shortlist supports it with a checkbox.