You cannot do it "without any third party software" but with zimbra, because your zimbra is already third party. :-)
First of all, don't use "command prompt" (CMD.EXE). Using it is a common mistake. Use just the file name of the application you want to start and, second parameter, it's command line. Please see:
If you really want it without third party, you should do it without third party. For example, you can use this:
In all cases, you will need some service serving as an entry point into the main system. It could be SMTP server, some Web service or mail Web site, etc.