nc -C mail.domain.com 25
HELO senderdomain.com
MAIL FROM:sender@example.org
RCPT TO:rcpt@example.com
DATA
From: sender@example.org
To: rcpt@example.com
Subject: subject example
Date: Fri, 10 Jan 2019 12:00:00 +0000
.
QUIT
testest test
nc -C mail.domain.com 25
HELO senderdomain.com
MAIL FROM:sender@example.org
RCPT TO:rcpt@example.com
DATA
From: sender@example.org
To: rcpt@example.com
Subject: subject example
Date: Fri, 10 Jan 2019 12:00:00 +0000
.
QUIT
testest test