POPcon downloads email ok, but can't reach my exchange server - what can I do?

Check the following:

• First check POPcon's settings on the SMTP tab. Is the SMTP-Server the network name of the machine you installed exchange server on? Don't use domain names (yourdomain.com) here, but network names (MYSERVER) or the IP of the server. 
• Exchange 5.5? Check if the "Exchange Internet Mail Service" is really running (control panel - services). If not, start it.
• Try to ping your exchange server computer from the one you installed POPcon (this also should work when both programs are installed on the same computer): Open a command window and type "PING EXCHANGE" or whatever you named your exchange server. If the exchange server computer does not answer, something with your network is not working and needs to be corrected.
• Try to telnet the Exchange server software: In the command window type "TELNET EXCHANGE 25" (again, use your own server name instead of EXCHANGE, the 25 is the port name, please keep that!). The telnet window should open and after a pause of several seconds, the exchange server should answer with something like "220 exchange.YOURDOMAIN.com ESMTP Server (Microsoft Exchange Internet Mail Service 5.5.2650.21) ready".
  If it does not answer:
• • Are you using a firewall software that might block port 25?
  • Antvirus software often includes provisions to block port 25 in order to keep virus code from using mail to propagate - McAfee is notorious for this but other antivirus software also includes options to block port 25. Disable that option in your antivirus software.
  • Antispam software: Check if antispam software is blocking the port 25.
  • Exchange 2010 or 2007: Check your Exchange server configuration. You can use your Exchange 2010 or Exchange 2007 configuration guides. Look closely at the configuration options of the receive connectors.
  • Exchange 2003 or 2000: Check your Exchange server configuration. You can use your Exchange 2000 or Exchange 2003 configuration guides. Look closely at the configuration options of the default virtual SMTP server and it's access tab.
  • Exchange 5.5: The caus is probably a configuration problem in Exchange's Internet Mail Service (IMS). Check the IMS-Configuration wether INBOUND connections are allowed in addition to outbound ones. Check if SMTP- connections are allowed without authentication and check if the domains you want to support are routed to "<inbound>".