You can do this with the help of your Customer Success Manager and your choice of email. Once you've decided on your preferred email address, let your CSM know. They will then provide some details for your IT team (or whoever sets up new emails) to provision and then once that's done, your email should be good to go!
Lots of our customers opt for something like "email@example.com" or similar because it will allow you to have multiple use cases running instead of "firstname.lastname@example.org" which you probably wouldn't want to use in your offboarding workflow!
Note: this email should be one that doesn't exist yet because theoretically employees could reply to the email so it's best they don't go to an existing inbox.