Step 1: Go to 'Listings' and click 'Manage' on your desired listing.

Step 2: Click on 'Integrations'.

Step 3: Click plus icon on top right to add your email integration.

Step 4: Select your email service.

In my case, it's 'Mailerlite', and click the down arrow to select groups from your email service where you want to store emails. And click the 'Add integration' to apply the changes.

Note: If you don't find your email service here, you should integrate your email service first. Click Here to know how to add your email service.