This command does not affect any parameters or previously entered
commands. It specifies no action other than that the receiver send a
"250 OK" reply.
This command has no effect on the reverse-path buffer, the forward-
path buffer, or the mail data buffer, and it may be issued at any
time. If a parameter string is specified, servers SHOULD ignore it.
快速浏览 RFC 会显示SMTP NOOP 命令。
NOOP
很好,但在开始新交易(发送新电子邮件)恕我直言之前RSET
更好。 无论如何用于测试从连接缓存中检索到的 SMTP 连接。sendmail
RSET
https://www.rfc-editor.org/rfc/rfc5321#section-4.1.1.5