Please contact your mail server admin and ask him to allow anonymous relay for the IP-address of your Allocatus/Project Server. Here are some starting points:
Exchange Server 2010
http://technet.microsoft.com/en-us/library/bb232021.aspx
Domino Server 8.5
http://publib.boulder.ibm.com/infocenter/domhelp/v8r0/index.jsp