Sending telnet smtp data command and ending with a period does not work
<p>I am stuck in my SSH telnet session, trying to test an SMTP connection, but when I enter a period to submit the data of a test email - nothing happens. 
I can end the session with the <kbd>control</kbd><kbd>]</kbd> - but I want to submit the data, not close the session. What am I missing?</p>

<p>Ubuntu 16.04 Client. Debian 8 server. Qmail.</p>

<pre><code>Connected to localhost.
Escape character is '^]'.
rcpt to: &lt;nospam@test.com&gt;

mail from: &lt;testmail@test.com&gt;
250 ok
rcpt to: &lt;nospam@test.com&gt;
250 ok
data
354 go ahead
From: Test_sender &lt;testmail@test.com&gt;
To: Test_receiver &lt;nospam@test.com&gt;
Subject: Just a stupid SMTP test

Just a test !

\r\n503 MAIL first (#5.5.1)&lt;return linefeed doesn't do anything either)
^Q^S
--&gt;.&lt;------------------------------------
(single period on one line-formatting issue)

^C
^Q
quit
exit
bye
</code></pre>