For sending/receiving messages to/from IC : You require IMS to be configured properly. IMS is the component keeps your exchange server to act as SMTP server.
For sending mails, let me know whether you are using DNS resolution or single SMTP host. If you are using DNS, you shd configure your IMS in the DNS database as an MX entry.
And also tell me abt the connectivity you have betwn your server & ISP setup.
Hari.