From: Bill Cole (postfixlists-070913billmail.scconsult.com)
Date: Mon Dec 10 2007 - 07:55:56 CST

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At 2:02 PM +0100 12/10/07, Rolf E. Sonneveld wrote:
>Hi,
>
>running Postfix v2.4.6.
>General info:
>- domain 'domain.nl' is listed in relay_domains; domain.nl is the
>main mail domain
>- mail-tcn.com is the IP level domain (hosts are within this domain)
>- domain 'lists.domain.nl' is listed in virtual_alias_domains
>- delivery for 'domain.nl' is partly done via LDAP lookups in Active Directory
>- for LDAP lookups two (AD) domain controllers are being used:
>dcad01.domain-tcn.com and dcad02.domain-tcn.com
>
>Delivery of mail for domains in relay_domains is via an LDAP lookup
>in Active Directory (AD) from within the transport map; the reason
>that the LDAP lookups are done on the transport level is that there
>are currently no secondary addresses defined in AD that can be used
>in the rewriting via the virtual_alias_maps.
>
>The problem is, that if the Active Directory server is not reachable
>from the Postfix system, mail starts bouncing, instead of being
>queued for later delivery.- When the AD servers are reachable, there
>is no problem at all.

[...]

>I thought, as the lookup shows '451 4.3.0 <joe.user1domain.com>:
>Temporary lookup failure' that mail would be requeued.

That is dependent on whatever is seeing that response. A lot of mail
software is broken.

>But a NDN was generated (and the problem got worse, as postmaster
>was aliased to an address in that same domain, causing another LDAP
>lookup and failure, causing another double-bounce etc. The queue
>filled up with NDN's.

What is actually generating those?

The log you included does not show Postfix generating any NDN
message. It is possible to eventually get them from persistent 4xx
failures, but any rationally configured mail software will requeue
and retry messages that get 4xx responses on their first attempt.

>Is there something I forgot to configure to get these temporary
>lookup failures result in a requeu instead of a bounce?

Probably, but not in Postfix. Whatever is talking to Postfix needs to
be reconfigured so that it requeues mail after 4xx rejections as it
should.

--
Bill Cole
billscconsult.com

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