This method is called by the System.Web.Security.Membership class with an e-mail address, which it uses to retrieve an associated user name from the SQL Server database specified in the ASP.NET application's configuration file (Web.config).

If more than one user in the membership database has the same e-mail address, the first user name encountered is returned. You can set the requiresUniqueEmail attribute to true in the application-configuration file to ensure that each e-mail address in the database is unique.

Leading and trailing spaces are trimmed from the email parameter value.