Why would you want to do this? This change may already be something that your users are sensitive about, so why not make the bulk update in Greenhouse as painless as possible.
What do I need to do? Open a Support Ticket and request a Bulk Update of your Organization User Email Addresses.
NOTE: You need to have a SuperUser role to make this request
What happens then? You will be provided a comma separated list (CSV) and asked to update the "New Email" column for all of your users and return it back to the Support team. Upon receipt, the bulk upload will be completed, and you will be notified.
Is there anything else that I need to know? Yes. All of the updated users will receive an email from Greenhouse to confirm their new email address. They will need to click the link within 24 hours of receipt for the confirmation to work, or it will have to be re-verified. Also, if the new email contact will be their primary, that will have to be manually updated in the user's "My Info"