Jason,
This has nothing to do with AUTHORITATIVE dns. I'm speculating this
is a problem with your choice of RECURSIVE (caching) name servers.
Realize, however, that without being on the box and looking at your
configuration, all I can do is speculate.
Mail .medvoice.com actually resolves to the mail server inside
through port forwarding.
Very typical.
It's not really named that just everything going to the mail ports
ends up there.
Understood. Again, very typical.
Would DNS still be an issue for sending internal mail.
Maybe, maybe not. It depends on your internal network setup and where
your server and workstations sit respective to each other. What's in
your server's /etc/resolv.conf file? On your windows workstation,
from the command prompt: ipconfig /all ... what "DNS Servers" are
listed here?
I ran top during one of these unresponsive email spats and noticed
that there are no smtp processes listed.
That just means there's no Postfix process in the busiest 20 or so
processes. Use the command "ps -aux" for a more complete process
view. That also means it's very unlikely your server is overloaded or
reaching process limits.
When someone initially connects to your mail server, typically the
first thing your mail server does is a reverse IP lookup on the person
connecting. Then, depending on your setup, it could also query a
number of RBL sources (Real Time Black Hole Lists) to see if the
sender is a known spammer. The more stuff that is done on that
initial connection, the more DNS lookups your server has to make and
the longer it takes to return the "OK" 220 prompt. That's why I'm
speculating this is a DNS issue. If my hunch is correct, your
/etc/resolv.conf will point to your ISP's recursive (caching) name
servers. Rarely do they perform well since they're shared amongst
hundreds/thousands/millions of users. For performance reasons,
you're better off running at least one caching name server of your own
inside your network - even on the server in question. While this is
only speculation on your problem, these methods also lean towards
"Best Practices" and are simple to implement.
-Ken
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