Email Relay and Email to Case Premium
You're currently using Email to Case Premium, have enabled (or are considering enabling) Email Relay and are wondering if there will be any impact to the application.
By default, Salesforce provides its own mail infrastructure for sending and receiving email messages.
In certain instances, organizations may choose to configure and activate Email Relay within Salesforce for outbound messages to show as originating from the organization's mail server rather than Salesforce's mail server.
Fortunately, Email to Case Premium is fully compatible with Email Relay. Enabling this feature will have no impact on sending outbound messages.
For more information on Email Relay and why an organization may consider enabling this feature, please review the following Salesforce knowledge article. Additionally, please review the article from Salesforce Ben, "Salesforce Email Relay: Prevent Your Emails Going to Spam."
Note: Organizations which have enabled Email Relaying along with Bounce Management or Email Security Compliance will need to ensure their mail server allows relaying of emails sent from Salesforce. If this has not been set up, emails from Salesforce may not be received by the intended recipient(s).