What happens when I subscribe customers from Shopify during initial sync?
When you have the setting enabled to sync existing Shopify subscribers that do not exist in Mailchimp, we will create a new subscriber in Mailchimp with the tag subscribed-from-shopify. You can use that tag to create a segment and remove the subscribers from any welcome automations so they don't receive a welcome automation.
Please note, if your audience is configured to support double opt-in, all existing subscribers in Shopify that do not exist in Mailchimp will receive an opt-in confirmation email from Mailchimp.
If you choose to not sync existing Shopify subscribers, they will have their accepts email marketing checkbox unchecked and be tagged with unsubscribed-by-mail-connect so you can identify those, if necessary.