To set an email status to unknown, follow these steps:
- Go to Constituent 360 > Constituents and search for the constituent you are concerned with.
- Click to edit their record.
- Edit the email status so that it is Unknown, then save the change
Alternatively, you can also use a variety of 3rd party email validation tools to check email addresses in bulk or one by one. By searching Google for the term "Free Email Validation Tools" you can find several options to choose from.