Timeout setting

Mark Andrews marka at isc.org
Fri Mar 26 22:01:10 UTC 2021

> On 26 Mar 2021, at 20:44, FUSTE Emmanuel <emmanuel.fuste at thalesgroup.com> wrote:
> Le 25/03/2021 à 22:15, Mark Andrews a écrit :
>> This is a bug in postfix. Temporary failures in the DNS are not supposed to result in permanent failure at the SMTP level.  SERVFAIL  is not NXDOMAIN.
> This is not a postfix bug. Temporary failure are perfectly handled by 
> postfix with a 450 SMTP temporary error, not a 550 permanent error.
> 450 4.7.1 Client host rejected: cannot find your reverse hostname, 
> []; from=<developer_bounces at insideapple.apple.com> 
> to=<XXX at example.com> proto=ESMTP helo=<rn2-msbadger07105.apple.com> 
> (total: 1)

Fine. I shouldn’t comment before my first cup of tea in the morning.

> You should have OS/network configuration problems. Such timeout are 
> completely unnatural.

Timeouts will happen.  Networks aren’t perfect.  Links can be congested.
Links can be noisy.  Hosts can be congested.  Hosts can be down.  There can
be routing failures.  There are those that configure their DNS such that it
requires excessive numbers of lookups to actually resolve an lookup.  Then
there are those that drop ICMP and fragmented packets breaking legitimate
traffic flows.  There is a reason there are 400 codes for DNS lookup failures.

> Emmanuel.
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at isc.org

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