A section similar to this is used for the
Incoming Mail (POP),
Outgoing Mail (SMTP),
SSH services. They are all based on the Port Service Plug-in. This is
displayed when you choose one of those services in the Service pop-up
menu in the Test Info pane.
These services all establish a connection to the requested server, then attempt to have a conversation with it, based on an established script of text to expect and appropriate responses. If Simon successfully makes it through the script, the check is considered a success. If, however, Simon can't connect, it doesn't receive anything, it doesn't receive the correct text, or it receives a recognized error situation, the check is deemed a failure (with the reason outlined in the logged error message).