我被困在我的 SSH telnet 会话中，试图测试 SMTP 连接，但是当我输入一个时间段来提交测试电子邮件的数据时 - 没有任何反应。我可以用control]- 结束会话，但我想提交数据，而不是关闭会话。我错过了什么？
Ubuntu 16.04 客户端。Debian 8 服务器。QQ邮箱。
Connected to localhost.
Escape character is '^]'.
rcpt to: <nospam@test.com>
mail from: <testmail@test.com>
250 ok
rcpt to: <nospam@test.com>
250 ok
data
354 go ahead
From: Test_sender <testmail@test.com>
To: Test_receiver <nospam@test.com>
Subject: Just a stupid SMTP test
Just a test !
\r\n503 MAIL first (#5.5.1)<return linefeed doesn't do anything either)
^Q^S
-->.<------------------------------------
(single period on one line-formatting issue)
^C
^Q
quit
exit
bye