What is the difference between Opt-In and Double Opt-In?

Overview

The best contact list is one filled with recipients who have requested that you send them something, but there are many kinds of mailing lists used in the industry, classified according to how reliably the recipients have indicated their willingness to be contacted.

CONFIRMED/DOUBLE OPT-IN

• A subscriber either manually inputs their email or checks a a box confirming they want to opt-in to the list.
• A confirmation email is sent to their email address.
• The subscriber must take an action (like clicking a link) in order to confirm that the address is valid.
• A welcome email is sent.
• Reliability: Most reliable method; default setting for new accounts.

NOTIFIED OPT-IN  

• A subscriber either manually inputs their email or checks a a box confirming they want to opt-in to the list.
• A welcome email is sent.
• Reliability: Second best method. 

SINGLE OPT-IN  

• A potential subscriber provides their email or checks a subscription box.
• Reliability: Low 

OPT-OUT (IMPLIED CONSENT)

• Email addresses are added despite the fact that the contact took no specific action to be added to the list, such as a pre-checked box when submitting their data on a form, as part of a checkout process or during account creation.
• Reliability: Poor. Under the Canadian Anti-SPAM Legislation, this type of consent expires in 6 months for leads and 24 months for active customers.