Allocate automatic role to am user in Nintex Process Manager

Unfortunately there's no way to set up an automatic rule to assign roles based on email domain in Process Manager, role assignment doesn't work that way in the system.

However, the quickest workaround for bulk assigning users to a role is using the Import Roles & Responsibilities function. 

Here's how:

Go to Admin > Roles
Click the settings icon on the top right and select Import Roles & Responsibilities
Download the CSV template, fill in the role name and add the users you want assigned
Upload the file and click Import

This would be much faster than adding users one by one, especially if you have a lot of users to assign. The CSV just needs the role name and the user's first and last name in the Users column.

For a longer term solution, we do have a feature on the roadmap that will allow roles to be matched to user properties in Entra ID, which could eventually support something closer to what you're looking for.