email - 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

快速谷歌检查，打开了这个( source ):

The simplest of these commands is NOOP, useful mostly in testing to avoid timeouts; it does nothing and can generate only a successful response, with no change in state...