Your System Administrator User can change the From Email Address for all automated emails that are sent via a Workflow Rule. In order to select an Email Address you will need to have at least one (1) Organization-Wide Email Address setup in your system.
Navigate to Setup > Workflow Rules
Select a Workflow Rule which has Email Alert actions
In this Example, we have a custom Workflow sending a series of emails after an unsold Appointment.
Select the Email Alert Action:
Scroll down to the From Address field, here you can choose from your Organization-Wide Addresses. If you do not see any email addresses in this Field, see also: How To Setup Organization-Wide Email Addresses
Helpful Hint: If Emails are being sent from the same Object (all Appointment related Emails) the Admin User can select to "Make this address the default From email address for this object's email alerts." This setting assures all Appointment emails are sent with the same From Address.