Manage System Users: Email domain, which contains underscore, is not valid

Steps to Reproduce:

1. Log in to Alfresco Explorer as admin user.
2. Open the Admin Console > Manage System Users page.
3. Click on the Create User button.
4. Enter any valid data into the First Name and the Last Name fields.
5. Enter an email address with an underscore in the domain, e.g. test1@test_1.com.
6. Click on the Next button.

Observed Result:

"Email format is not valid" message is displayed. Please, see the attached screen1.png.

Expected Result:

The email is correct. It should be processed successfully. No error should occur.

Regression:

• The issue was not reproduced on Enterprise v4.2.1 (r63452-b50).
• The issue seems to be a regression since MNT-8444, i.e. the error came from the released 4.2.2 (r70245-b51).

Additional Note:

• The issue was not reproduced in Share - the email domain was processed correctly via Share Admin Console.
• Set the higher "Major" priority because of the regression.

ChristinaSh