I can't confirm destination email address as it is a printer

I have a printer that I have connected to the cloud using the manufacturers online service.

They printer has an associated email address that I can then send an email to and it will print successfully.

The printer email address is not intuitive so I want to use my own domain and printer name.

I’ve set up a destination address that forwards to the printer but I can’t verify the printers email address as the email prints off and there is no way for me to instigate the “verify email address” action indicated required.

How can I achieve this as there appears to be no way in the printer manufacturers app that allows me to view the verification email before printing it.