Opt-in
A recipient actively indicating that they want messages from a sender, such as by ticking an unchecked box or submitting a signup form.
What it means
M3AAWG defines opt-in as the process of a recipient indicating that they wish to receive messages from a sender, and calls verifiably clear, conspicuous and informed opt-in consent the best practice for messaging permission. It describes three levels: single opt-in, single opt-in with a notification, and confirmed (double) opt-in.
Details decide whether an opt-in counts. Yahoo warns against subscribing users through an opt-in checkbox that is checked automatically, and France's CNIL says a pre-ticked box is forbidden for collecting consent. M3AAWG adds that the signup should state which lists the person joins and how often they will hear from you, and that consent for one purpose or channel does not carry over to another.
Keep a record of every opt-in: date, source, IP and the wording shown.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
All 432 terms in the glossaryThe wiki: blocklists and bounce codes