Hi jjohn1022,
In the default SD.Email Monitor package, as Michael.George suggested, in the Process Message model, there is a component entitled "Set User Info-Guest User". It follows the "Search User (by email Address)" component. It is a Single Value Mapping component. It looks like a cylinder with green and red arrows in the bottom right corner.
1. Open that component and click on the mapping defintion ellipsis
2. You will see a few different lines with a circles attached on the right side of the mapping table.
3. Find the one called Reference Name, and double-click on the line, you will note that this is configured to a constant value, guest@logicbase.com. This is the guest account you are looking for.
4. Simply modify this to meet your requirements
5. Save and republish and this should work fine.
Please note that these instructions are based on a default installation of 7.1 Sp1. Up until 7.5 this was pretty consistent. The component you are looking for should always be just in front, or very close to the Submit Incident component.
I hope this helps.