I don't see the emails from the list.

[Bill Campbell]

On Sat, Sep 29, 2007, Jay R. Ashworth wrote:
>On Sat, Sep 29, 2007 at 06:40:35PM -0700, Bill Campbell wrote:
>> On Sat, Sep 29, 2007, Jay R. Ashworth wrote:
>> >On Sat, Sep 29, 2007 at 06:18:00PM -0700, Bill Campbell wrote:
>> >> Our largest regional ISP customer only lists a single MX server
>> >> which handles all their incoming mail.  If there's a problem with
>> >> that machine, we can change the DNS to have it go to another
>> >> server in minutes.
>> >
>> >DNS caching client-ISP-side doesn't cause you problems there?
>> 
>> Not that I've ever noticed.  We're running djbdns' dnscache on the machine.
>> We use very aggressive DNSRBLs *AFTER* first checking an extensive DNSRBL
>> white list.  Since postfix doesn't support DNSRBL whitelisting, I've
>> enabled the tcp dictionary, and written a little tcp server in python that
>> handles this, caching lookups as the whitelists change very slowly.
>
>I wasn't clear: you're talking about public-to-the-Internet MX records.
>
>If you change the MX record in DNS, unless you commonly run it with a
>wildly low TTL, people in teh outside world will lose the ability to
>get mail *in*, no?  And remember: some ISP caching servers are reputed
>to *ignore* low TTLs, rewriting them up.

This hasn't been a problem.  The TTL is less than an hour.  We
could switch one of the cluster machines or perhaps the openldap
server to primary MX duty, and bring up a suitable interface in
about fifteen minutes if necessary.  They have multiple backbone
providers which minimizes the possibitlites of connection loss.

In the worst case, if they were totally out of commission for a
period of time, I could change the DNS on one of the backup DNS
servers on our networks, and add a secondary MX record to one or
more of our mail servers to catch and hold mail until they were
back up and running.

Bill
--
INTERNET:   bill at celestial.com  Bill Campbell; Celestial Software LLC
URL: http://www.celestial.com/  PO Box 820; 6641 E. Mercer Way
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