Auszug aus: http://www.keylabs.com/news/links/news_21217AdToolbox.pdf
This one is more of a technique than a tool but helpful nonetheless for its intended purpose. Mail flows through the Internet using the Simple Mail Transport Protocol (SMTP). For troubleshooting Internet e-mail, a manual SMTP session is the best way to isolate the problem because you get to see exactly what is going on. The first step is to use nslookup or dig to find out the name and IP address of a mail exchanger for the destination domain. Pretend for a minute that the "mx" query mentioned above for somedomain.com came back with a name of mailhub.somedomain.com and an IP address of A.B.C.D. IP addresses are really numbers (not letters) but you understand the idea. From there a network administrator would telnet to port 25 on the server at A.B.C.D. If everything is working the administrator would see a "220" message, the friendly name of the mail exchanger, whether SMTP or ESMTP is supported, and the name and version of mail exchanger software running on the server. The session below illustrates how to send a mail message manually. I know the thought would never crossed your mind, but please note that this is for educational purposes only and not for sending funny e-mail messages to your friends from famous people. The parts in bold are what you would need to type.
root@Linux:/ > telnet mailhub.somedomain.com 25 Trying A.B.C.D... Connected to mailhub.somedomain.com. Escape character is '^]'. 220 mailhub.somedomain.com ESMTP Exim 4.04 Wed, 13 Nov 2002 16:27:42 -0700 helo someotherdomain.com 250 mailhub.somedomain.com Hello someotherdomain.com [E.F.G.H] mail from:<Jim@someotherdomain.com> 250 OK rcpt to:<Joe@somedomain.com> 250 Accepted data 354 Enter message, ending with "." on a line by itself Subject:Test Message This is a test message. . 250 OK id=18C6vd-0005Ey-00 quit 221 mailhub.somedomain.com closing connection Connection closed by foreign host root@Linux:/ >
Joe@somedomain.com should get an e-mail from Jim@someotherdomain.com or you will have to do more troubleshooting to isolate the problem.