eXtended Account Managing Software: able to manage e-mail accounts for several domains and sites
Fast, rock stable, secure, GPL, feature filled and multiplatform ESMTP/POP3/FINGER/POPSYNC server
XMail Queue Manager
gives you full control over the multi level nested mail queue of the server. You can track messages in their different states (sending, resending, frozen). Statistics tell you about the number of spooled messages. Its crossplatform remote feature allows you to manage queues of servers without GUI.
Z1 SecureMail Gateway
(commercial) a central, server-based software solution which provides encryption and digital signatures for the entire email traffic of an organization