smtp via telnet

Most people would have know of this very useful way to test a mail server.Just in case you dont ,read below :P(i am no expert in this also)

open up your dos prompt and key in the command to connect to your mail server
1)telnet {ip address} 25 <-Press enter
2)helo {pcname} <-Press enter
3)mail from:{sender's email address,must be valid} <-Press enter
4)rcpt to:{recipient's email address} <-Press enter
5)data <-Press enter and enter your email message
6). <-press enter

step 6 is to end the process...usually i will press "enter . enter" to end the process.your mail will be send...:)
good way to troubleshoot..if the relay of mail has been blocked etc...