What is single opt-in vs double opt-in?
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Single opt-in (SOI) means when someone fills in your signup form and hits Submit, they're on your list. Done. No confirmation step. Fast, frictionless, and the reason many senders choose it for high-volume list building.
Double opt-in (DOI) adds one step: after the form, a confirmation email goes out, and the subscriber has to click a link to verify they actually own the address. Only confirmed clicks result in a subscription.
The tradeoff is list size vs. list quality. SOI converts more form submissions to subscribers. DOI filters out typos, bots, and addresses that were never going to engage. The 70% who confirm with DOI are worth more than the 100% you'd add with SOI unverified. They also give you stronger consent documentation under GDPR.
For most email programs, double opt-in is the better default. If you're weighing whether single opt-in makes sense for your situation, read about when SOI is actually acceptable and what you need to have in place if you go that route.
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