Opt-In, also known as subscribe. Explicitly requesting to receive information from a company via e-mail. All responsible email marketers ensure that only users who have opted in receive their communication. If you haven’t opted in – it’s SPAM! There are several common forms of opt-in email: Unconfirmed opt-in, confirmed opt-in and opt-out.
Unconfirmed opt-in means that someone gives his email address for some reason, either filling out an online form or something else. Then this email address is not confirmed, meaning that nothing has been done to confirm that the address belongs to the certain person, and can therefore, when received, be seen as a spam. Other reasons for an email to be a spam can be typos, among other things.
The difference between confirmed and unconfirmed opt-in is seen in the title itself. Confirmed opt-in is in some way confirmed by the users who have agreed to be subscribed to a given mailing list. The confirmation usually occurs when, after subscribing, you get an email in which there is a link which you have to click on in order to confirm it is actually you. Other way of confirming can be just to send and email reply to the company you are subscribing to.
Opt-out means that a person is put in a mailing list, without they wanting that. Afterwards they have the option to request to be put out.