The Sponsor Confirmation email is a system-generated email for an initiative.  As a result, it cannot be modified.  It is a hard coded default email with the following information:

[Date, Time (PT)]

First Name, Last Name
Company Name
Address Line 1
City, State, Zip

The following amount summarizes your contribution:
Sponsorship Amount: [Amt]

[Account Name] contact information:
Email address: [Event Contact Email]

[Text from Sponsorship Caption field, which is located in Website Features of the event]

Because the text cannot be edited, you may wish to Disable the Sponsor Confirmation Email