Objective:
By default, your personal email address in Salesforce is listed as the return address. You can simply change this to another preferred email address, for instance, a shared mailbox email address. Nevertheless, return address default to personal email address is an out-of-box behavior from Salesforce, and there is currently no workaround for admin to alter it.
Note: The return address is used when you are creating a new email or sending a reply email within Salesforce.
1. In Salesforce, go to your profile by clicking the avatar (view profile) at the top right corner. Then, go to Settings.
2. This opens a new tab in Salesforce to display your Personal Information. Navigate to Email > My Email Settings.
3. Under My Email Settings, you can update the following:
Return Address - Use any preferred email address
Automatic BCC - Select Off if you do not want to be BCC'ed when sending emails within Salesforce.
Signature - The signature you would like to use when emailing in Salesforce.
4. Make your change, and then click Save to save your changes.