Enable double opt-in
This article explains how to configure the "double opt-in" feature.
MailChimp settings
MailChimp audience has the option "Enable double opt-in". Enable this option if you want to send contacts an opt-in confirmation email before subscribe them to the audience.
You also should set options: "Default From name", "Default From email address", "Default Email subject". MailChimp uses these data in the confirmation email.
Image - Audience settings, Audience name and defaults.
Ultimate Member settings
Ultimate Member has the option "Enable double opt-in" that can enable the "double opt-in" feature for a certain connection if it is not enabled in the audience settings.
Note: this option has lower priority then the setting "Enable double opt-in" in the audience settings.
Image - The connection settings on wp-admin > Ultimate Member > MailChimp > Edit.
Member approval
The extension adds a contact to the audience after the member's approval. The extension doesn't add new members if their status is pending admin or email verification until these members will be approved. This depends on the "Registration Status" role setting.
Image - User role settings on wp-admin > Ultimate Member > User Roles > Edit
The extension adds a contact immediately if the "Auto Approve" option is chosen.
Members should visit their mailbox and click the "Activate your Account" button in the email to approve their accounts if the "Require Email Activation" option is chosen.
Image - Account Activation email example.
Administrators should manually approve new members if the "Require Admin Review" option is chosen.
Once the member is approved the extension adds a contact and MailChimp sends the opt-in confirmation email.
Image - Opt-in confirmation email example.
Related articles:
About Double Opt-In
Single Opt-In vs. Double Opt-In