SMTP 'NOOP' 命令的用途是什么？

Question

SMTP 规范中 NOOP 的目的是什么？

它说：

   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.

   Syntax:

      noop = "NOOP" [ SP String ] CRLF

Answer 1

一个快速的谷歌检查，打开了这个（来源）：

这些命令中最简单的是 NOOP，主要用于测试以避免超时；它什么都不做，只能产生一个成功的响应，状态没有变化......