There are some websites on the internet which allows you to send emails to any person. By using fake mail sender u can send emails to any email id by any email id (fake email id not necessary to exists). Suppose you know the email id of a person A. You want to send an email from the email id of person A. You can use these fake emailsender website to do that. You can send email by any email id either it exists or not.
try this fake mail sender website : mail.anonymizer