It is suggested to secure all communications traffic between devices and the Lotus Notes Traveler server to avoid any over the air security breaches. Depending on your environment, this can be achieved by enabling SSL encryption for the Lotus Domino HTTP server or reverse proxy, or by using a VPN. If you are using a Lotus Notes Traveler High Availability (HA) configuration then all servers in the HA pool must be configured in the same way (either all should use SSL or none).
Once the SSL is enabled, you can use https://hostname to access the server instead of http://hostname. You can either use Domino self-signed SSL certificates or third-party SSL certificates to configure SSL on the Domino HTTP server. Third party trusted SSL certificates are recommended as some devices will not tolerate an untrusted certificate and will not be able to connect to a server using a self-signed untrusted certificate.
For steps to enable SSL on Lotus Domino server, see the server documentation http://publib.boulder.ibm.com/infocenter/domhelp/v8r0/index.jsp?topic=%2Fcom.ibm.help.domino.admin85.doc%2FH_ABOUT_SETTING_UP_SSL_ON_A_SERVER.html