HTTPS is used to encrypt all data transmitted between a browser and the SpamTitan web server. This is especially important for publicly accessible servers to prevent passwords being compromised. To use HTTPS you will require an SSL certificate, if you do not have an SSL certificate please see this document on how to create or import an SSL certificate: http://helpdesk.spamtitan.com/support/solutions/articles/4000013127-ssl
To enable HTTP go to Settings > Access/Authentication > Web Management Protocol.
Select the certificate you wish to use and then click save. HTTP is now enabled. We recommend disabling HTTP if you have HTTPS enabled to prevent unencrypted access to the web interface.