Without SSLTo test a POP3 account from command line follow these steps. This will connect to the POP3 server using telnet, list the available emails, and retrieve the first one.
telnet <your-email-server>:110 Connected to your-email-server-ip... Escape character is '^]'. user <your-mail-server-username> pass <your-mail-server-pass> list retr 1 quit
With SSLIf you are getting the following error, you will need to access your POP3 server using SSL
user <user-mail-server-username> - ERR Command is not valid in this state.To use SSL, use
OpenSSLto connect to the server
openssl s_client -crlf -connect <your-email-server>:995 .... + OK The Microsoft Exchange POP3 service is ready. user <your-mail-server-username> +OK pass <your-mail-server-pass> +OK User successfully logged on. list retr 1 quit