Telnet to the desired port on the host when you are certain it is working properly, and see what comes back. You can enter just an identifying portion of a SimpleExpect or Expect keyword.
For example, if you expect to get "220 hostname.domain.com Imail v1.3" back from the host, you could use "220 host" as a response string (i.e. SimpleExpect=220 host, or Expect=^220 host).
Note: Some services are based on binary protocols (such as DNS) and will not provide you with a simple response string to use. You can use a packet capture tool to view these types of responses.