Email clients like netscape do not authenticate properly Netscape Messeneger 3.x, 4.x and other clients cannot authenticate. Some Email clients such as Netscape Messenger require that the @ symbol be substituted by a % sign in order to authenticate properly. In addition, you need check the box "My server requires authentication" if you have authentication enabled. You will also have to specify the "Log On Using" option. Enter as follows: UserID%Domain.com and the password. Verify that you substitute the @ symbol with the % sign, if it does not log into the account, update the email client.