Single opt-in vs. double opt-in

Every Mailchimp audience uses one of two signup methods:

• Single opt-in - a contact is added the moment they sign up. Lower friction and faster list growth, but a higher chance of invalid addresses or unengaged contacts landing on your list.
• Double opt-in - a contact must actively click a confirmation link before they're actually added to the audience. Slower growth, but stronger list quality and clear, documented proof of consent - recommended if deliverability or complaint rates are a concern.

Good list hygiene - removing long-unengaged contacts, watching bounce and complaint rates, only emailing people who've genuinely opted in - protects the sender reputation that domain authentication is built to establish. The two topics reinforce each other. 

How the CDP handles consent

The CDP tracks each guest's consent status and keeps the Mailchimp audience it's connected to aligned with it - when a guest's consent changes in the CDP, that change is reflected in the connected Mailchimp audience.

For this reason, we recommend working with a single primary Mailchimp audience per property or brand wherever possible, organized using tags and segments rather than split across multiple audiences. Besides simplifying consent management, this also avoids being billed twice for the same contact if they end up duplicated across audiences.

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Additional material

Mailchimp Help Center 

• About Duplicate Contacts
• Single Opt-in vs. Double Opt-in