You can edit your one-time and first-time recurring email receipt by going to the Receipt Email tab of your campaign editor.
This section will provide an editor to amend this template.
From the Variables dropdown, you can select and add placeholders to the email body that will be automatically replaced with information from the donation before it's sent to the donor.
Donorbox also sends donation receipts after charging your recurring donors each month. You can customize the content of these email receipts by clicking Engage and then the Receipts link on the left.