You are using Email to Case Premium and would like to know how it prioritizes Contacts to be associated with a Case when duplicate Contacts exist.
When an inbound email is processed by Email to Case Premium, we check the From Line of the inbound email message to determine who will be selected as the Case Contact.
Currently, Email to Case Premium prioritizes on the following:
If your organization intentionally retains duplicate contacts, and would like Email to Case Premium to prioritize a specific Contact record over others, this can be achieved by implementing the following:
1. If you haven't already, define separate Contact record types for the duplicate contact records.
2. Update your Organization Wide Default sharing model on the Contact object to be Private.
3. For the Email to Case Premium context user (defined under Setup > Develop > Email Services > Email to Case Premium), update this user's profile to disable the "Modify All Data" and "View All Data" permissions under the System Permissions section. You may have to clone the standard System Admin profile to do this.
4. Within the Object Settings for this profile, enable only the Contact record type this user should be able to access.
5. Create a new public group for the Context User (specifically for sharing rule purposes in the next step).
6. Creating a sharing rule on the Contact object to provide this public group will sufficient access to Contacts matching that Contact record type.
From there, the Email to Case Premium context user will only be able to access Contacts for case association of that particular record type.
Please note, this KB article is provided as-is and customization with Sharing Rules / User Profiles is not supported under the scope of support provided with the Email to Case Premium application. For further assistance, please contact your Salesforce administrator, Salesforce implementation partner, or your Internet Creations Account Executive to inquire about professional services.