An email list signup process requiring a subscriber to confirm their email address via a follow-up confirmation email before being fully added to a mailing list, as opposed to being added immediately upon submitting a signup form.
Why it matters
Double opt-in significantly improves list quality by filtering out mistyped email addresses, bots, and people who didn't genuinely intend to subscribe — at the cost of some drop-off from real subscribers who don't complete the confirmation step, a real tradeoff between list size and list quality.
In a sentence
"We moved to double opt-in after noticing our list had accumulated a lot of invalid addresses that were quietly hurting deliverability."
Related terms
- Antonyms: Single opt-in (a subscriber is added to a list immediately upon signup, with no separate confirmation step required).
- Often confused with: Opt-in/Opt-out (Category 8, Part One) — that entry describes the general concept of proactive consent versus default inclusion; double opt-in is a specific technical implementation of the opt-in consent process, adding a confirmation step on top of the initial signup).