SMTP server error message

SMTP server error message

[Eli Zaretskii]

Hi,

I need some help from the SMTP experts here.

Since about a couple of days ago, some of the messages I send via
smtpmail fail because the SMTP server sends this response, after the
message is sent to it:

  451 4.0.0 Spam filter end message failed - server - license [slot 1]

When this response comes in, smtpmail bails out.  This only happens
with about 25% probability, and in particular if I immediately resend,
the message is sent with no problems.

What does that response mean, and what can I do to avoid it (apart of
hacking smtpmail)?

TIA

Re: SMTP server error message

[Achim Gratz]

Eli Zaretskii writes:
> Since about a couple of days ago, some of the messages I send via
> smtpmail fail because the SMTP server sends this response, after the
> message is sent to it:
>
>   451 4.0.0 Spam filter end message failed - server - license [slot 1]

The 451 repsonse means there has been an error on the server while
processing the message and the pending action has been aborted.

> When this response comes in, smtpmail bails out.  This only happens
> with about 25% probability, and in particular if I immediately resend,
> the message is sent with no problems.

You might be talking to an address that uses load-balancing over
multiple servers and only one of those has a problem.  Another
possibility is that whatever is doing the spam filtering doesn't respond
(quickly enough).

> What does that response mean, and what can I do to avoid it (apart of
> hacking smtpmail)?

Getting a 451 means, "Sorry, didn't work out this time.  Come back later
if you still want to."  Most SMTP servers would now enter exponential
backoff for re-delivery attempts, most MTA will simply bow out and let
the user handle the problem.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Wavetables for the Terratec KOMPLEXER:
http://Synth.Stromeko.net/Downloads.html#KomplexerWaves

Re: SMTP server error message

[Florian Weimer]

* Eli Zaretskii:

>   451 4.0.0 Spam filter end message failed - server - license [slot 1]

> What does that response mean, and what can I do to avoid it (apart
> of hacking smtpmail)?

Looks like a problem at your ISP.  They probably have a cluster node
that is broken, and sending again hits a node that works.

SMTP server error message

[Stephen J. Turnbull]

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.

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.

You don't say which SMTP server you're talking to.  If it's an
outbound relay, you might talk to the sysadmin and see if your host
can be permanently whitelisted.

Re: SMTP server error message

[Stefan Monnier]

> Getting a 451 means, "Sorry, didn't work out this time.  Come back later
> if you still want to."  Most SMTP servers would now enter exponential
> backoff for re-delivery attempts, most MTA will simply bow out and let
> the user handle the problem.

Did you mean "MUA"?  Or what is the difference between an MTA and an
SMTP server?


        Stefan

Re: SMTP server error message

[Eli Zaretskii]

> From: "Stephen J. Turnbull" <stephen@xemacs.org>
> Cc: emacs-devel@gnu.org
> 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.

Re: SMTP server error message

[Eli Zaretskii]

> From: Achim Gratz <Stromeko@nexgo.de>
> Date: Sat, 31 May 2014 16:16:33 +0200
> 
> Getting a 451 means, "Sorry, didn't work out this time.  Come back later
> if you still want to."  Most SMTP servers would now enter exponential
> backoff for re-delivery attempts, most MTA will simply bow out and let
> the user handle the problem.

Thanks.  So you are saying I have nothing better to do than perhaps
talk to my ISP representatives and urge them to fix the problem?

Re: SMTP server error message

[Eli Zaretskii]

> From: Florian Weimer <fw@deneb.enyo.de>
> Cc: emacs-devel@gnu.org
> Date: Sat, 31 May 2014 16:27:47 +0200
> 
> * Eli Zaretskii:
> 
> >   451 4.0.0 Spam filter end message failed - server - license [slot 1]
> 
> > What does that response mean, and what can I do to avoid it (apart
> > of hacking smtpmail)?
> 
> Looks like a problem at your ISP.  They probably have a cluster node
> that is broken, and sending again hits a node that works.

Thanks.

Re: SMTP server error message

[Achim Gratz]

Stefan Monnier writes:
>> Getting a 451 means, "Sorry, didn't work out this time.  Come back later
>> if you still want to."  Most SMTP servers would now enter exponential
>> backoff for re-delivery attempts, most MTA will simply bow out and let
>> the user handle the problem.
>
> Did you mean "MUA"?  Or what is the difference between an MTA and an
> SMTP server?

Yes, sorry for the typo.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Factory and User Sound Singles for Waldorf rackAttack:
http://Synth.Stromeko.net/Downloads.html#WaldorfSounds

Re: SMTP server error message

[Achim Gratz]

Eli Zaretskii writes:
> Thanks.  So you are saying I have nothing better to do than perhaps
> talk to my ISP representatives and urge them to fix the problem?

It's at least worth trying to send a mail to postmaster (or whatever
their administrative contact) so they can check their logs and perhaps
tell you what's going on or even just fix it.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Wavetables for the Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables

Re: SMTP server error message

[Stephen J. Turnbull]

Eli Zaretskii writes:
 > > From: "Stephen J. Turnbull" <stephen@xemacs.org>
 > > Cc: emacs-devel@gnu.org
 > > 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]

Oops, should have investigated more carefully instead of going by
memory.  Here's the RFC 5321 definition of status code 451:

451     Requested action aborted: local error in processing

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

Sorry, I shouldn't have mentioned the MTA policy or emacs-devel.
They're irrelevant since you're using smtpmail.

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

Greylisting affects all incoming calls to the server, not just you.
If it's just you, it's not greylisting.

 > [greylisting timing] doesn't seem to match what I see:
 > It's my ISP's SMTP server.

OK, I just guessed entirely wrong.  Very sorry!  Between the
definition of 451, and those two facts, we can rule out greylisting.

451 means an intermittent problem at your ISP.  The "one broken node
in the cluster" hypothesis sounds plausible to me, but in any case
since the server is at your ISP, they should fix their server.  It's
not smtpmail, since the transaction is completing with a proper
response code, it's the server.

To save you (and maybe others) some grief, smtpmail could retry on any
status code matching "4[0-9][0-9]", that's what an SMTP client is
supposed to do.  Probably in most cases waiting a few seconds and
trying once should be enough when you're talking only to your ISP.

Re: SMTP server error message

[Eli Zaretskii]

> From: "Stephen J. Turnbull" <stephen@xemacs.org>
> Cc: emacs-devel@gnu.org
> Date: Sun, 01 Jun 2014 03:18:11 +0900
> 
> 451 means an intermittent problem at your ISP.  The "one broken node
> in the cluster" hypothesis sounds plausible to me, but in any case
> since the server is at your ISP, they should fix their server.  It's
> not smtpmail, since the transaction is completing with a proper
> response code, it's the server.

OK, I guess I'll collect the names of the servers that return this
error, and if they are the same every time, will send a note to
postmaster.

> To save you (and maybe others) some grief, smtpmail could retry on any
> status code matching "4[0-9][0-9]", that's what an SMTP client is
> supposed to do.  Probably in most cases waiting a few seconds and
> trying once should be enough when you're talking only to your ISP.

I will try that as well.  Are all 4XX codes indeed of this nature?

Re: SMTP server error message

[Stephen J. Turnbull]

Eli Zaretskii writes:

 > I will try that as well.  Are all 4XX codes indeed of this nature?

Yes, all 4xx codes are an invitation to try again, they indicate a
transient glitch with the server (server couldn't allocate memory,
spamchecker crashed, that kind of thing).

There's no way to know when the server expects the problem to get
fixed, but for smtpmail I would guess that if it isn't fixed in a few
seconds, you may as well give up, and try by hand later.  Having
smtpmail retry multiple times in the background over several hours is
probably more programming than it's worth.