I am wondering what email should be used when setting up an API only user for a Content Syndication purpose?
Should it be an email from the vendor?
An email that uniquely identifies a human in case you need to contact someone. Technically the email doesn't need to be emailable (since no welcome message goes out) but it's best if it is. Of course if you have a separate repository of contacts you could choose a dummy address like firstname.lastname@example.org.