Cannot login to Webmail

When using the Webmail, make sure your email address was created in the control panel using all lowercase, ie.

If your email address has mixed case letters, login into the Control Panel and rename the email address by going into the e-mail section, and reset the username on your account to be the same using all lowecase.

Since email servers and most clients are not case sensitive, changing your email to all lowercase should not affect your regular email service.