Cannot Send E-mails

I have just installed v 5.0.0 as a trial with a view to evaluating it prior to purchase. I have gone through the initial setup and have successfully managed to get the system to pull in e-mails from the mailbox on my exchange server (different server to the one running Service Desk).

However I am trying to reply to the test requests but when I hit the send button on the reply form I get a "Sending Notification Failed" message.

The Exchange server is set to allow relaying from the server running SD and it is on a local (private) LAN to the SD server. I have tried it with authentication on and off with the same response.

I have also tried setting the outgoing server to the SD server which has a SMTP service and Virtual Server running.

Any ideas would be appreciated.

Thanks