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Name Service error but resolver is working

On our IMAP service host I am seeing messages in the mailq similar to
the following:

50DFB12B2F7 7501 Tue Nov 6 17:22:42 MAILER-DAEMON
(delivery temporarily suspended: Host or domain name not found. Name
service error for name=mx31.harte-lyne.ca type=MX: Host not found, try
again)

Postfix on the IMAP host is configured to route outgoing mail through
MX31. And mail is flowing in and out of the IMAP system. Most things
are being delivered. But a few messages are stuck in the mail queue
with this error and I cannot figure out what the problem with them is.

I have confirmed that the DNS resolver on both the IMAP host and MX31
are working. I can ping from the IMAP host to MX31. On the IMAP host
I can use swaks to successfully send mail via the localhost. On the
IMAP host I can also use swaks to successfully send mail via MX31.
The test messages both arrived in the destination mailbox on the IMAP
host.

I do not understand what the DNS issue is, but I cannot flush
messages with this error.

Comments

Re: Name Service error but resolver is working

By Paul Enlund at 11/07/2018 - 12:22

Hi

Maybe related to some of your NS not responding certainly from the UK
that is

dig  -t a mx31.harte-lyne.ca  @dns01.harte-lyne.ca  OK

dig  -t a mx31.harte-lyne.ca  @dns02.harte-lyne.ca     No response

dig  -t a mx31.harte-lyne.ca  @dns03.harte-lyne.ca   several seconds to
respond

dig  -t a mx31.harte-lyne.ca  @dns04.harte-lyne.ca   No response

On 07/11/2018 16:06, James B. Byrne wrote:

Re: Name Service error but resolver is working

By Viktor Dukhovni at 11/07/2018 - 11:39

Note that the lookup in question is "MX", not "A". This means that
the message has a recipient address of " ... at mx31 dot harte-lyne.ca",
rather than "localpart@harte-lyne.ca".

While harte-lyne.ca has working MX records, and the "A" record of
"mx31" resolves just fine, there are issues with *MX* lookups for
"mx31.harte-lyne.ca".

<a href="http://dnsviz.net/d/mx31.harte-lyne.ca/dnssec/" title="http://dnsviz.net/d/mx31.harte-lyne.ca/dnssec/">http://dnsviz.net/d/mx31.harte-lyne.ca/dnssec/</a>

Re: Name Service error but resolver is working

By Wietse Venema at 11/07/2018 - 11:30

James B. Byrne:
Are your services chrooted?

$ postconf -F '*/unix/chroot' | grep '\= y'

Those will not use the name server configured in /etc/resolv.conf,
but rather, the one configured in $queue_directory/etc/resolv.conf.

Wietse

Re: Name Service error but resolver is working

By byrnejb at 11/07/2018 - 12:17

No. We do not use chrooted services:

# postconf -F '*/unix/chroot'
anvil/unix/chroot = n
bounce/unix/chroot = n
cleanup/unix/chroot = n
defer/unix/chroot = n
discard/unix/chroot = n
error/unix/chroot = n
flush/unix/chroot = n
lmtp/unix/chroot = n
local/unix/chroot = n
proxymap/unix/chroot = n
proxywrite/unix/chroot = n
relay/unix/chroot = n
retry/unix/chroot = n
rewrite/unix/chroot = n
scache/unix/chroot = n
showq/unix/chroot = n
smtp/unix/chroot = n
tlsmgr/unix/chroot = n
trace/unix/chroot = n
verify/unix/chroot = n
virtual/unix/chroot = n
retry/unix/chroot = n

RE: Name Service error but resolver is working

By Deeztek.com Support at 11/07/2018 - 11:13

It's probably backscatter:

<a href="http://www.postfix.org/BACKSCATTER_README.html" title="http://www.postfix.org/BACKSCATTER_README.html">http://www.postfix.org/BACKSCATTER_README.html</a>

On our IMAP service host I am seeing messages in the mailq similar to the following:

50DFB12B2F7 7501 Tue Nov 6 17:22:42 MAILER-DAEMON
(delivery temporarily suspended: Host or domain name not found. Name service error for name=mx31.harte-lyne.ca type=MX: Host not found, try
again)

Postfix on the IMAP host is configured to route outgoing mail through MX31. And mail is flowing in and out of the IMAP system. Most things are being delivered. But a few messages are stuck in the mail queue with this error and I cannot figure out what the problem with them is.

I have confirmed that the DNS resolver on both the IMAP host and MX31 are working. I can ping from the IMAP host to MX31. On the IMAP host I can use swaks to successfully send mail via the localhost. On the IMAP host I can also use swaks to successfully send mail via MX31.
The test messages both arrived in the destination mailbox on the IMAP host.

I do not understand what the DNS issue is, but I cannot flush messages with this error.