When a customer enters their details into your Bigcommerce website, they'll be automatically synced to MailChimp through MailSync.
To prevent customers from receiving marketing emails from you without consent, they will receive an email from MailChimp asking them to opt-in to your mailing list.
This double opt-in process helps to verify that you have permission to send mail to a subscriber.
There's no need to change anything on your end. If you want to learn more about MailChimp's double opt-in process, you can learn more here.
If you've successfully connected your Bigcommerce account to MailSync and are pushing customers into MailChimp, their status will automatically be set to Pending.
Any marketing emails you send will not be delivered to your Pending customers until they have opted in to your email list.
The customer will receive an email asking them to confirm their subscription to your mailing list. If they do not accept, their status will remain as Pending.
Pending customers are not searchable and do not appear in any lists in MailChimp for privacy reasons.
You can find more information about MailChimp's double opt-in process here.