Double opt-in
A signup that is only complete once the subscriber clicks a link or replies to a confirmation email, proving the address is theirs and the request was real.
What it means
M3AAWG calls confirmed opt-in, also known as double opt-in or closed-loop subscription, the highest standard of opt-in. After the address is submitted, a confirmation message asks the person to act (click a link or reply), and no subscription mail is sent until they do. This keeps typos and maliciously submitted addresses off the list. The confirmation should be simple and free of advertising, and a changed address should be confirmed the same way.
Yahoo recommends asking new subscribers to click to confirm, and Spamhaus's standard recommendation is to mail only addresses that have gone through confirmed opt-in, which also keeps spam traps off a list.
Confirmed opt-in gives you proof of consent: keep the confirmation record.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- M3AAWG Sender Best Common Practices, version 4.0 (August 2026)m3aawg.org
- Yahoo Sender Hub: Sender requirements and recommendationssenders.yahooinc.com
- Spamhaus FAQ: Marketing emailspamhaus.org
- Spamhaus: ZEN blocklistspamhaus.org
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