telnet domain.com 25
helo domain
mail from: <someone@somewhere.net>
rcpt to: <whoever@wherever.com>
data
Reply-To: <person@place.org>
Subject: whatever

This is the message. Note that there is a blank line between the headers
(Reply-To, Subject, etc.) and the message body. The blank line MUST be
present.

Bye.

P.S. To end the message, enter a single dot at the beginning of a line.

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