Using older mail clients with MailSite Some Macintosh and older Windows email clients cannot authenticate using the login format user@domain.com, which is typically required when logging in to virtual domains in MailSite. These clients must use an alternate login format. Some email clients, including Outlook Express on the Macintosh, cannot use the @ symbol when authenticating using a complete email address. Users of these clients users must substitute the % character for @. For example, instead of entering the login name: johndoe@rockliffe.com users should use the login name: johndoe%rockliffe.com (We have verified that Eudora 5.x does not require this symbol change.)