Create some users on your site Navigate to "Site administration" > "Users" > "Upload users" Download the example CSV file and modify it: Add have some entries that: Correspond to email addresses for the users in step 1 Have different first names and last names to the users from step 1 Press "Upload users" Set "Upload type" to "Update existing users only" Set "Existing user details" to "Override with file" (it appears after you set upload type) "Match on email address" to "Yes" Press "Upload users" Verify the users are shown as updated in the table Navigate to "Site administration" > "Users" > "Browse a list of users" and verify the users were updated Navigate to "Site administration" > "Plugins" > "Authentication" > "Manage authentication" and under "Common settings" turn on " Allow accounts with same email " Edit one of the user accounts to have the same email as another one Edit the CSV, modifying the row having the email address associated with the two students (change the first name or last name to something new) Repeat the process of uploading the CSV Verify a warning is displayed for the row with the email that maps to multiple users and that those users are not updated