The first thing to do is to open a connection from your computer to your mail server.

telnet mail.domain.ext 25

Trying ???.???.???.???...
Connected to mail.domain.ext.
Escape character is '^]'.
220 mail.domain.ext ESMTP Sendmail version-number; date+time+gmtoffset

You will then need to delcare where you are sending the email from:

HELO local.domain.name

250 mail.domain.ext Hello local.domain.name [loc.al.i.p], pleased to meet you

don't worry too much about your local domain name although you really should use your exact fully qualified domain name as seen by the outside world the mail server has no choice but to take your word for it as of RFC822-RFC1123.

Now give your email address:

MAIL FROM: mail@domain.ext

250 2.1.0 mail@domain.ext... Sender ok

Now give the recipients address:

RCPT TO: mail@otherdomain.ext

250 2.1.0 mail@otherdomain.ext... Recipient ok

To start composing the message issue the command

DATA

If you want a subject for your email type

Subject: type subject here

then press enter twice (these are needed to conform to RFC 882)

You may now proceed to type the body of your message

Just type the body of the message as it should appear with any punctuation, new lines etc as needed.

To tell the mail server that you have completed the message enter a single "." on a line on it's own.

.

250 2.0.0 ???????? Message accepted for delivery

You can close the connection by issuing:

QUIT

221 2.0.0 mail.domain.ext closing connection
Connection closed by foreign host