Any Systems Administrator worth his or her salt needs to use the good old fashioned Telnet application. Why? Despite its archaic look and feel, and lack of security, telnet serves at least one IMPERATIVE function in an IT environment: connecting to port 25 of the company email server! Port 25 is the default port for SMTP data traffic, probably the single most important port in the Internet universe, except for maybe port 80 (http, or the web). You can also use it to test the IMAP port:143.
That's right, although there are many ways to skin a cat when testing for email problems, one of the quickest, sure fire ways to find out if there is a general problem with sending/receiving emails is to telnet to the email server. For example, if several usually busy company employees mention, "We haven't received any email since 10:00 AM", and it's 12:30 PM ... well, you better start troubleshooting. Of course, in reality it's easy to remote desktop or VNC, etc to the server directly and start looking around. Also, if something bad has indeed happened, a good monitoring system should alert you right away to a router or Windows Exchange Service failure, etc. But a real quick test from a Windows XP or Windows 2003 Server would be to open up a command prompt (go to Start, type 'cmd') and type "telnet mailserhostname.yourdomain.com 25" to test SMTP.
From a Windows Vista system, then, it should be easy too, right? Well, maybe, but first understand that Telnet is not operable by default. If you open a command prompt, and try the above, you may get this: " 'telnet' is not recognized as an internal or external command or batch file'. Translated, you are being told indirectly: "turn on Telnet"
So, go to the Vista Start menu/Control Panel /Programs, "Turn Windows Features On or Off". Scroll down to Telnet Client (not the Server, you do not want to be a telnet server) and check it, hit OK. The feature update is seen in a small window. Now it's time to telnet.
Open the Vista menu (or Start menu) and in the "Start Search" window, type 'telnet'. You then enter the simple, although slightly changed instructions. Type 'o', hit Enter. "O" stands for open. Imagine that! Then type in the full email server hostname that is being tested, followed by '25' (unless for some reason the default port has been changed)
After that you should see either a successful or failed connection. The former means you have issues elsewhere as this particular SMTP connection worked, but the latter would mean your SMTP appears to be in distress. Note: this test should be done via both internal and external connections, if possible, in case the issue affects a certain segment of your routing or Windows domain scheme, etc.
So, in summary, telnet is a very useful tool to explore possible SMTP connectivity issues with a mail server. Once telnet is enabled or installed, this whole process takes under 10 seconds. And when dealing with company or any organization's email, that means a great deal.