smtp-cache problem

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smtp-cache problem

Thomas Minor
Hello,

I might have a problem with the smtp_connection cache.
Regarding documentation, the cache is enabled on demand by default.

I found a peer site, which is also driven by postfix, with uses greylisting.
I have some 3000 mails to send to this particular server, which starts the session
by greylisting my server. Since postfix uses the smtp_connection_cache by default,
it reuses the connection which receives one greylisting temp fail after the other.
This seems to triggers the $smtpd_hard_error_limit on the other site. My server
continues to use now dead connection until the cache limits take effect.

I tend to assume, that this is a bug and maybe a configurable amount of errors should
trigger the sending postfix to abandon a connection.

Did i miss any configuration options here or do you agree?

Yours,

--Thomas


--

  Thomas Minor, Development

  H & R Netzwerk GmbH
  Am Königsweg 9
  48599 Gronau-Epe

  Sitz:            Gronau / Westf.
  Handelsregister: Amtsgericht Coesfeld, HRB 5886
  Geschäftsführer: Harald Beine

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Re: smtp-cache problem

Wietse Venema
Thomas Minor:
> Hello,
>
> I might have a problem with the smtp_connection cache.
> Regarding documentation, the cache is enabled on demand by default.

This question was already answered. Use youe search engine.

        Wietse
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Re: smtp-cache problem

Thomas Minor

Hmm, ok,

I did search but found nothing. I'll check again.


--Thomas


Am 22.02.2017 um 21:51 schrieb Wietse Venema:
Thomas Minor:
Hello,

I might have a problem with the smtp_connection cache.
Regarding documentation, the cache is enabled on demand by default.
This question was already answered. Use youe search engine.

	Wietse

-- 

  Thomas Minor, Development

  H & R Netzwerk GmbH
  Am Königsweg 9
  48599 Gronau-Epe

  Sitz:            Gronau / Westf.
  Handelsregister: Amtsgericht Coesfeld, HRB 5886
  Geschäftsführer: Harald Beine

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Re: smtp-cache problem

Alex JOST-2
Am 24.02.2017 um 09:03 schrieb Thomas Minor:
> Hmm, ok,
>
> I did search but found nothing. I'll check again.

http://marc.info/?t=148763167000002&r=1&w=2

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Alex JOST
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Re: smtp-cache problem

Thomas Minor

Ahh, ok, now i got it.

I thought, a similar question was already answered but it seems I missed the answer
on my own question, sorry. It stayed in my outgoing box an I assumed, there was a
delivery problem. That's why I sent it twice.


Back to the problem, as I pointed out, the delivery attempts to the other postfix system
from my server started to fail after hitting the hard error limit so it refused to accept any
further message on this connection. It seems either the other server did not close the
connection or my server did nod recognize the connection end, since my server tried
to send mail across the old connection.

After I disabled the connection cache, sending mails worked as supposed. They got greylisted
first and
could be delivered at the second attempt. Due to earlier problems with this particular
server i configured my server in a way
, that it splits a mail with multiple recipients in separate
mails btw.

I think, that postfix as a server should close the connection after its hard error limit is hit, since it
won't accept any mails on this connection anyway. And, on the other side, postfix as a client
should not reuse a dead connection.

Yours,


--Thomas


Am 24.02.2017 um 12:31 schrieb Alex JOST:
Am 24.02.2017 um 09:03 schrieb Thomas Minor:
Hmm, ok,

I did search but found nothing. I'll check again.

http://marc.info/?t=148763167000002&r=1&w=2


-- 

  Thomas Minor, Development

  H & R Netzwerk GmbH
  Am Königsweg 9
  48599 Gronau-Epe

  Sitz:            Gronau / Westf.
  Handelsregister: Amtsgericht Coesfeld, HRB 5886
  Geschäftsführer: Harald Beine

--
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Re: smtp-cache problem

Viktor Dukhovni

> On Feb 26, 2017, at 5:56 PM, Thomas Minor <[hidden email]> wrote:
>
> And, on the other side, postfix as a client
> should not reuse a dead connection.

Postfix (somewhat obviously) cannot "reuse" a closed connection.
The other server must have kept open.

It is in principle possible to add a feature to limit re-use of
connections exceed a given count of consecutive re-use attempts
without delivering a single message.

However, as Wietse pointed out, rather similar symptoms occur
with multi-recipient mail, the real issue is that greylisting
generates many self-inflicted "errors" on the receiving side,
and the best solution is for sites that use greylisting to not
impose error count limits.

--
        Viktor.

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Re: smtp-cache problem

Thomas Minor
Hi Viktor,


thanks for the answer. I'll try to suggest this to the other servers admin team.
Since I do not know if they consider this, I'll stick to disabled default connection reuse.

I'm interested which end of the connection is responsible of the problem, I'll setup a test
for this sometime.

--Thomas


Am 27.02.2017 um 00:15 schrieb Viktor Dukhovni:

>> On Feb 26, 2017, at 5:56 PM, Thomas Minor <[hidden email]> wrote:
>>
>> And, on the other side, postfix as a client
>> should not reuse a dead connection.
> Postfix (somewhat obviously) cannot "reuse" a closed connection.
> The other server must have kept open.
>
> It is in principle possible to add a feature to limit re-use of
> connections exceed a given count of consecutive re-use attempts
> without delivering a single message.
>
> However, as Wietse pointed out, rather similar symptoms occur
> with multi-recipient mail, the real issue is that greylisting
> generates many self-inflicted "errors" on the receiving side,
> and the best solution is for sites that use greylisting to not
> impose error count limits.
>

--

  Thomas Minor, Development

  H & R Netzwerk GmbH
  Am Königsweg 9
  48599 Gronau-Epe

  Sitz:            Gronau / Westf.
  Handelsregister: Amtsgericht Coesfeld, HRB 5886
  Geschäftsführer: Harald Beine

--

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