This article details how to disable the email input prompt during user enrollment.
Disabling the Allow user-initiated key generation option for a user policy removes the requirement for a user to enter an email address during enrollment as well as preventing users from creating new keys after installation. This can be advantageous when managed clients are only using PGP Whole Disk Encryption or all client keys for email are being managed on the server using Server Key Mode (SKM).
To disable user-initiated key generation