To access listener configuration in WebAdmin, first click on the service tab (SMTP Receiving, POP3, IMAP, WebMail, WebAdmin, FTP Back-up&Restore, CLI, POP3 Proxy, IMAP Proxy or Webmail Proxy). A list of the already defined listeners (if any) will be displayed under the dedicated section Listeners, sorted by their IP addresses.
Editing one of the existing listeners will result in accessing two configuration pages: General and SSL Settings. The same pages will also be displayed when hitting the Add Listener button and choosing the Advanced Config option.
Example: SMTP Receiving listeners

No matter if you are adding or editing a listener, no matter on what service tab you are on, the same parameters are available in two dedicated pages: General and SSL Settings.

See subsections of current page for more details:
Configuring General ParametersSSL Parameters for Listeners
