Primary domain does not login account without fully qualified e-mail address Primary domain login requires a fully qualified e-mail address to successfully login. Setting up a mail server with more than 1 Shared IP address, you need to make sure that the first IP that is assigned to your Network card is not use for a virtual domain. If you assign the primary IP of your network card to a virtual domain, it will act as if it's the new Default domain. Running a mail server with multiple IP address bound to your network card and assigning a static IP address to a virtual domain, allows clients to connect directly to that domain and login with just their Account name and Password. Without having to enter their complete fully qualified e-mail address to login as you have to with a shared IP address. If you are sharing 1 IP address for all your domains, then your clients will have to login with their fully qualified e-mail address.