Volunteers at a nonprofit in the US can be given an email address, and they can be given a title. This is a pretty common practice in many small to mid-sized nonprofits. It has a nice upside of valuing your best volunteers, increasing their buy-in to the nonprofit, and can help them community their value/role with your org externally much more quickly. Someone booking a venue for an event sending emails from their personal gmail account versesis a big difference. Just make clear what expectations are, and have a clear time/path for taking that email account and title back.
However if you are a for-profit entity then you would find yourself in a lot of hot water with the IRS.