To add letterheads, headers, and footers while sending invoices by email from BUSY, follow these steps:
1. Go to the email configuration settings in BUSY.
2. Enter your personal name as the sender.
3. Specify any header or footer text you want to include, such as greetings or regards.
4. Save the configuration.
5. Send an email to test the settings and see if the letterheads, headers, and footers are included.
Note: It is important to note that BUSY may not have the option to add letterheads, headers, and footers specifically for invoices.