Re: SMTP server error message

[Eli Zaretskii]

> From: "Stephen J. Turnbull" <address@hidden>
> Cc: address@hidden
> Date: Sat, 31 May 2014 23:47:07 +0900
> 
> Eli Zaretskii writes:
> 
>  >   451 4.0.0 Spam filter end message failed - server - license [slot 1]
> 
> Greylisting.  The idea is that a real MTA will retry (it's a temporary
> failure, which means you are being invited to try again later with
> exactly the same address and message data), while a spammer will just
> move on to the next victim's address.  Reduces spam by about 75%, but
> most MTAs wait about 4 hours to retry, which is a long time for a list
> like emacs-devel.

It's not coming from the list, though.  It comes from the SMTP server
my Emacs is talking to in order to send email.

Are you saying that the SMTP server is trying to greylist me
personally?  Why would it want to do that?

> The greylisting MTA normally whitelists you immediately for a period
> of time (typically 24 hours) after the first (temporary) failure.
> This may explain your 25% failure rate, the others are within the
> auto-whitelist period.

This doesn't seem to match what I see: If I send the same message
several times one after the other, one in 3 or 4 gets this error, the
other go through.  So there doesn't seem to be any significant time
period during which I'm whitelisted.

> You don't say which SMTP server you're talking to.

It's my ISP's SMTP server.