What Do The Terms “Opt-in” And “Double Opt-in” Mean?

Opt-in is when someone actively gives you their email address to send them something.  Examples include having a notebook by your cash register to have people jot down their contact information or subscribing to an e-newsletter or email correspondence online.

Double opt-in is when a company receives a request to subscribe to an email address, they reply to that email for verification that the request did in fact come from there.  This ensures that the request was not set-up from a third party for malicious intent.  Most companies use this method to keep their list active and to avoid any spam penalties.

[Story Found at Expert Business Source]