The single opt-in method is simple. It's probably what you think of when you think of signing up to email marketing. A contact fills out your signup form, clicks submit, and their information is saved in your audience. Behind the scenes, for record keeping purposes, the form saves important information like the contact's IP address and the date and time they signed up.

A single opt-in is a one-step process and only requires a person to enter their email address one time in the signup box on a website. No confirmation is required, and they immediately become a subscriber.

Single opt-in (SOI) is a subscription process where a new email address is added to your mailing list without requiring the owner of that email address to confirm definitively that they knowingly and willingly opted in.