Re: Re: Postfix smtp freezing

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Ken,

You are correct, resolve.conf does list my isp's dns 250.171.3.65 which is qwest. The internal windows workstations also point o the isp's dns server.
Can I setup a cashing dns server on the mail server itself??

PS: I just wanted to say thanks to everyone who has helped me so far.

-jr

Ken Price wrote:
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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