FYI. I moved your post to Products section of the site where most of our product experts are.
Also, I see you have three different accounts on the Community. Can you add the words 'Primary' next to the job title of your primary account, so we know where / how to contact you, if we need to. Thank you,
You cannot do this. Only Email Address is available to use for the sending email.
I believe there are potential workarounds and you can do a search for "secondary email".