Port 25 is used for SMTP. It stands for Simple Mail Transfer Protocol. With this protocol you can send email. The commands you can use can be found in RFC 821. In this example we are going to send an email.
First start a new client. This can be done by clicking on the client button or selecting Sockets and New Client.
Type the name of your mail server in the textbox behind server. This will be something like mail.myprovider.com. In the textbox port, type 25 and press return or click on Connect.
In the received area you can see if the connection is successful. When it is, type first a HELO computername. Where computername is the name of your computer or type something else. The mailserver will send you a response.
Then type MAIL FROM:<emailaddress> You will get a 220 OK back. Type RCPT TO:<emailaddress> where emailaddress is the emailaddress of the person you want to send mail to. When you get an OK signal back, type DATA At this point you can enter your mail message. When you are ready, give a return followed by a . (point) and give a second return. This indicates the end of the message. To close the connection type QUIT.
A typical transaction is listed below. S is the server and C is the client.
S: 220 BBN-UNIX.ARPA Simple Mail Transfer
Service Ready
C: HELO USC-ISIF.ARPA
S: 250 BBN-UNIX.ARPA
C: MAIL FROM:<Smith@USC-ISIF.ARPA>
S: 250 OK
C: RCPT TO:<Jones@BBN-UNIX.ARPA>
S: 250 OK
C: RCPT TO:<Green@BBN-UNIX.ARPA>
S: 550 No such user here
C: RCPT TO:<Brown@BBN-UNIX.ARPA>
S: 250 OK
C: DATA
S: 354 Start mail input; end with .
C: Blah blah blah...
C: ...etc. etc. etc.
C: .
S: 250 OK
C: QUIT
S: 221 BBN-UNIX.ARPA Service closing
transmission channel