Re: [PLUG] user's mail not being delivered, odd error

[Rich Kulawiec <rsk@gsp.org>]

On Wed, Feb 27, 2019 at 05:16:04PM -0500, Rich Freeman wrote:
> Wait, why would you be depending on external DNS servers?  Aren't you
> filtering all outgoing traffic anyway?  So, if you whitelist every
> mail server you let your mailserver talk to, then why would you need
> to rely on outside DNS lookups in the first place?  :)

I'm having a great deal of difficulty parsing this message: I don't
understand why you've mentioned traffic filtering or whitelisting, because
neither of those are related to the kind of problem I'm describing.

However, (nearly) all mail systems, except for those specially configured
for dedicated tasks and/or specifically configured to *not* use DNS
(yes, there are use cases for this), rely on external DNS servers.
Sometimes they rely on internal DNS servers.  If there are issues
related to either of those, then one of the common symptoms is a mail
queue that won't flush.

---rsk
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