What is the return-path in email?
When an email is sent to an invalid email address, that email will bounce, meaning it won’t land in an inbox. Many emails that bounce will have a return path embedded in the email information – this return path is the address that will be alerted about the bounced email.
The return path is inserted in the original email header. It’s similar to a formal letter where the return-path is typically written at the rear of the letter.