Notifications do not work for users with uppercase or special characters in the username

Steps to Reproduce:

1. Create an user with an uppercase character in the user name.
2. Log in with the new user.
3. Create a Service Desk request.

Expected Results:

Service Desk sends a notification for the user as usual.

Actual Results:

Service Desk does not send any notifications for the reporter.

Same problem happens for users with "special" characters, like '.' or '@'