Via command prompt go to AppManager/bin/troubleshooting directory and execute the POPtest file with the usage below.
Usage :
popTest.bat [HostName / Ip] [Port Number] [username] [password]
[HostName / Ip] HostName or Ipaddress of machine where SMTP server is running
[Port Number] Port number of the smtp server
[username] User name for connecting to pop server
[password] Password for connecting to pop server