How can I send mail to a SMTP server using Telnet?

A. A. As with POP3, SMTP messages can also be sent using telnet by connecting to port 25 on the SMTP server, e.g.

C:\> telnet 25

Once connected you optionally announce to the server who you are (this is needed for some SMTP servers)

helo <domain>
e.g. helo

vrfy <user account>
e.g. vrfy john

Once you are verified you can commence to write an e-mail message. The first command is mail and you specify who it is from, e.g.

mail from:<[email protected]>

The address has to be in <>. Next you have to specify who will be receiving the message using rcpt, e.g.

rcpt to:<[email protected]>

The from and to have been completed you can start the body of the message using the data command. You have to create the header information in the first lines of the message. Once you have completed the message enter a '.' on a blank link and the message will be sent. Below is an example creating a message.

Click here to view image

As you can see I entered a from, date, to and a subject and then entered the body of the text. Make sure you don't make a mistake as if you backspace this is enterpreted as a bad character and will be rejected. If a message is rejected a rejection will be send to the address specified in the "mail from:<...>" and for this reason you should only ever put your e-mail address. Although I have used a different address as a joke you should NEVER do this.

Below is how the message looks when received in Outlook 98:

Click here to view image

The above shows how easy it is to send a message and make it look from a different address but if you examined the header you would easily see it was sent from a different mail server and rumble its a fake (and a very bad one)!

I shall be adding future entries describing how to STOP people sending mail from your server (as they probably can at the moment).

For full information on SMTP and the commands you can use see Request For Comments 821.

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