Using port 80 is not recommended for productive use as passwords and data are going to be transmitted in plain text.
Consult the documentation coming with the product (google: domino infocenter). eg: http://publib.boulder.ibm.com/infocenter/domhelp/v8r0/topic/com.ibm.help.domino.admin85.doc/H_ABOUT_SETTING_UP_SSL_ON_A_SERVER.html
If using this in a productive environment you may want to double check by contracting IBM to check your setup and implement best practices configuration if necessary.