What is single opt-in vs double opt-in?

Single opt-in (SOI) adds subscribers to your list immediately upon form submission. User enters email, clicks submit, they're subscribed. It's frictionless-no additional steps required-which maximizes conversion from form to subscriber. The downside: fake emails, typos, and bots all make it onto your list without verification.

Double opt-in (DOI) requires confirmation. User enters email, receives a confirmation email, must click a link to verify intent. Only confirmed clicks result in subscription. This extra step verifies email ownership (reducing typos and abuse), confirms genuine intent (reducing complaints), and creates documented proof of consent (satisfying GDPR's accountability principle).

The tradeoff is conversion rate vs. list quality. SOI might convert 90% of form submissions to subscribers; DOI might convert 60-70% (many never complete confirmation). But that DOI 70% represents verified, genuinely interested subscribers-they're worth more than SOI's unverified mass. Double opt-in is recommended for most email programs because the quality improvement in engagement and deliverability outweighs the quantity reduction at signup.