When taking online email sign-ups, you can choose between two models for adding addresses to your list:

• In the Opt-In method, when someone submits their address, you immediately add them to your list. In this model, a confirmation email should be sent to the address, informing them that they have been added, but no reciprocal confirmation is required
• In the Double Opt-In method, when someone submits their address, you send an email that includes a confirmation link which the recipient must click on in order to be placed on the mailing list. Double Opt-In allows you to fully verify the validity of the email address and prevents third parties from submitting addresses, while cutting down on spam complaints and bouncing emails. However, this more rigorous model will limit your list growth, which is why many organizations use simple Opt-In.