Telnet for OS X - Sending Mail (port 25)

To run a telnet session and send mail, do the following...

1) Launch the Terminal application from /Applications/Utilities/
2) Type telnet smtp.reseller.net 25 [Return]
3) Type helo [Return] (not necessary on all mail servers)
4) Type mail from: sender's address [Return]
5) Type rcpt to: recipient's address [Return]
6) Type data [Return]
7) To set a subject field (not essential) type subject: subject title [Return]
8) Type the message body content and finish the message by typing a full stop on a new line and press [Return]

An example of an SMTP session is shown below...