If you're collecting newsletter subscribers on your store's checkout page you'll want to ensure these new contacts are synced to Mailchimp instead of Jilt.
Disable Jilt's checkout sync
WooCommerce and Easy Digital Downloads stores
For WooCommerce and Easy Digital Downloads stores, this setting is found in Jilt under Settings > Shop settings > Storefront settings. Remove the checkmark next to the "Show an opt in at checkout to ask for consent for marketing emails" setting.
Disable checkout opt-in on WooCommerce and Easy Digital Downloads
For Shopify stores it's not necessary to make any changes in Jilt as Shopify has a built-in feature for capturing consent via their checkout page.
Enable Mailchimp's checkout sync
For WooCommerce stores using the Mailchimp for WooCommerce plugin, the checkout page settings are available in your WordPress admin at WooCommerce > Mailchimp > Audience settings.
Easy Digital Downloads stores
For Easy Digital Downloads stores using the Mailchimp plugin, the checkout page settings are available in your WordPress admin at Downloads > Settings > Extensions > Mailchimp.
For Shopify stores using the ShopSync app recommendation, the default checkout page takes care of the sync for you. Customers who opt-in at checkout are automatically synced back to your Mailchimp account.
Continue to Step 5: Migrate autoresponders.