When using the PCSchool Email control if you have correctly entered the SMTP server address and the user is still unable to handshake with that server then this may be caused by the Exchange Servers internal settings. To ensure that Exchange Server 2010 is correctly configured then have your IT log into the Mail Server.
Click on Mail Flow on the left hand side.
Click on Receive Connections.
Edit the Connector called Internal Relay
Add the users IP address into the box that lists all the IPs that are entitled to relay emails through this server.