Re: some mails bounce with 'Name or service not known'

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some mails bounce with 'Name or service not known'
\ Sven Putze (12 Jan 2008)
. \ (Wietse Venema) (12 Jan 2008)

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Subject:	Re: some mails bounce with 'Name or service not known'
Group:	Postfix-users
From:	(Wietse Venema)
Date:	12 Jan 2008

Sven Putze:
> Every now and then Postfix doesn't deliver mail (it's bounced directly,
> not deferred) and the reason is logged with
>
> <account>: [dom.ain]: Name or service not known

Postfix receives a DNS reply that the domain has no MX record.
Postfix also receives a DNS reply that the domain has no A record.

> But the target domain "dom.ain" is an existing one (and can be
> successfully "digged". If the sender tries again Postfix can find
> "dom.ain" and delivers the mail (as most of the time to this domain).

There are endless possibilities.

- Some Linux boxes distribute Postfix with chroot turned on, so
that Postfix uses a different resolv.conf file than normal programs.
Distributing Postfix with chroot on is an endless source of grief.

- You're using some crappy local DNS server that provides false
replies under load.

- Some up-stream crappy DNS server (perhaps in a cheap router)
provides false replies under load.

Solution: point Postfix's resolv.conf to a real DNS server.

> First question: is direct bouncing a wanted behaviour and if so, is
> there a chance to get those mails in the deferred queue instead?

Yes, if the DNS says that the destination does not exist, then
bouncing is desirable. You can configure Postfix (soft_bounce=yes)
to always put mail back into the queue but that is not a permanent
solution.

> Second question: does Postfix have problems with DNS lookups when
> spambots are causing stress?

Postfix does not have the problem. The problem is that some
crappy DNS server produces bogus replies.

Wietse