In some cases, you might need to create a public group of Salesforce users in order to meet your company's Salesforce permission structure. Here's how you can create a public group.
1) Go to Setup > Administer > Manage Users > Public Groups > click the New button
2) On the New Group page, enter the following information:
Label: Soapbox Mailer
Group Name: Soapbox_Mailer
Grant Access Using Hierarchies: Yes
Selected Members: User: Soapbox Mailer Email Tracking Guest User
3) Click the Save button