If you are writing an SMTP agent, you might find it instructive to learn to speak SMTP yourself, both to aid debugging and to get a feel for what is happening "under the hood" when Exchange receives a message from the internet. This is a lot easier than it might sound. Open the Run dialog box (press Window + R) and enter "telnet localhost smtp" (or substitute the name of your Gateway server in place of localhost). This will open a window where you can talk with the server. The server will begin the conversation by sending a banner, such as:
220 mail.contoso.com ready at Thu, 23 Feb 2006 17:46:23 -0800
You may continue the conversation by entering the following commands, one line at a time. Note that there is a blank line in the middle - it's important. Just press enter to send the blank line:
ehlo console
mail from: sender@contoso.com
rcpt to: recipient@contoso.com
data
From: sender@contoso.com
Subject: Test Message
This a test message.
.
quit
Source:
http://msexchangeteam.com/archive/2006/07/14/428324.aspx