How to exclude email addresses from being added to cases automatically
Email to Case Premium includes a feature that looks at the To: and CC: fields on an inbound email and can automatically add a Contact Role or Case Team Member if a Contact or User match is found on the email address, this includes auto-created addresses. Depending on your configuration, additional email addresses may be added to the Additional To and CC fields. You may want to prevent this from happening for specific email addresses or domains.
Email addresses in the Case Creation Settings are automatically excluded from being added as Contact Roles or Case Team Members. Thus, every email address that forwards to Salesforce should be defined in Case Creation Settings to be excluded. Additionally, you can specify other email addresses or domains in the Exclude List within the Email to Case Premium configuration. You can mix and match email addresses and domains, separating each with a comma.
Navigate to Setup > View Installed Packages > and click Configure next to Email to Case Premium. Choose Inbound Configuration from the Jump To menu in the upper right and scroll to the bottom of the page.