Opt in email is a term used when someone is given the option to receive "bulk" email, that is, email that is sent to many people at the same time. Typically, this is some sort of mailing list

Electronic mailing list

An electronic mailing list is a special usage of email that allows for widespread distribution of information to many Internet users. It is similar to a traditional mailing list — a list of names and addresses — as might be kept by an organization for sending publications to...

, newsletter, or advertising. Obtaining permission before sending email is critical because without it, the email is Unsolicited Bulk Email, better known as spam.

There are several common forms of opt-in email:

Unconfirmed opt-in

A new subscriber first gives his or her address to the list software (for instance, on a Web page), but no steps are taken to make sure that this address actually belongs to the person. This can cause email from the mailing list to be considered spam because simple typos of the email address can cause the email to be sent to someone else. Malicious subscriptions are also possible, as are subscriptions that are due to spammers forging email addresses that are sent to the email address used to subscribe to the mailing list.

Confirmed opt-in (COI)

A new subscriber asks to be subscribed to the mailing list, but unlike unconfirmed opt-in, a confirmation email is sent to verify it was really them. Many believe the person must not be added to the mailing list unless an explicit step is taken, such as clicking a special web link or sending back a reply email. This ensures that no person can subscribe someone else out of malice or error. Mail system administrators and non-spam mailing list operators refer to this as confirmed subscription or closed-loop opt-in.

Some marketers call closed loop opt-in "double opt-in." This term was coined by marketers in the late 90s to differentiate it from what they call single opt-in, where a new subscriber to an email list gets a confirmation email telling them they will begin to receive emails if they take no action. Some marketers contend that double opt-in is like asking for permission twice and that it constitutes unnecessary interference with someone who has already said they want to hear from the marketer. The term double opt-in has also been co-opted by spammers, diluting its value.

Opt-out

Instead of giving people the option to be put in the list, they are automatically put in and have the option to be taken out.

Address Authentication

Email address authentication is a technique for validating that a person claiming to possess a particular email address actually does so. This is normally done by sending an email containing a token to the address, and requiring that the party being authenticated supply that token before the authentication proceeds. The email containing the token is usually worded so as to explain the situation to the recipient and discourage them from supplying the token (often via visiting a URL

Uniform Resource Locator

In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....

) unless they in fact were attempting to authenticate.

For example, suppose that one party, Alice, operates a website on which visitors can make accounts to participate or gain access to content. Another party, Bob, comes to that website and creates an account. Bob supplies an email address at which he can be contacted, but Alice does not yet know that Bob is being truthful (consciously or not) about the address. Alice sends a token to Bob's email address for an authentication request, asking Bob to click on a particular URL if and only if the recipient of the mail was making an account on Alice's website. Bob receives the mail and clicks the URL, demonstrating to Alice that he controls the email address he claimed to have. If instead a hostile party, Chuck, were to visit Alice's website attempting to masquerade as Bob, he would be unable to complete the account registration process because the confirmation would be sent to Bob's email address, to which Chuck does not have access.

This degree of email authentication is considered by many anti-spam

Spam (electronic)

Spam is the use of electronic messaging systems to send unsolicited bulk messages indiscriminately...

 advocates to be the minimum degree necessary for any opt-in email advertising

Advertising

Advertising is a form of communication used to persuade an audience to take some action with respect to products, ideas, or services. Most commonly, the desired result is to drive consumer behavior with respect to a commercial offering, although political and ideological advertising is also common...

or other ongoing email communication.

Related Books

• Opt In Email List Building by John S. Rhodes
• The Complete Guide to E-mail Marketing by Bruce C. Brown
• E-Mail Marketing For Dummies by John Arnold