For Unassigned Extensions
This article assumes that the Admin has added Unassigned Extensions to the account already. To assign multiple unassigned extensions to users using the same email address, the "User requires unique Email ID" option needs to be disabled.
1. Log In to your RingCentral Account as an Admin.
2. Go to Admin Portal > Users > User List > Unassigned Extension > Select a specific extension you wish to modify.
3. Go to Set Up Options on the bottom of the Unassigned Extension page. Select "Setup by the admin on behalf of the user".
4. The "User requires unique email ID" option is enabled by default. Un-check the box to disable.
While this resolves the issue on a user level, unique email IDs are still required for bulk user account/extension creation through csv template uploads.