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2002 May 31 18:44

The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

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Re: [vox-tech] Change mail host, lose e-mails?
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Re: [vox-tech] Change mail host, lose e-mails?



Within BIND config for your domains, you can specify a value for mutiple
mail servers. If you know one host will become your new mail server, just
make sure that the new server has a "better" value than the older one and
mail clients should try for the one with the higher importance.

E.G.:
passwall.com.           86400   IN MX   50      mail.passwall.com.
passwall.com.           86400   IN MX   100     woodrow.estoremakers.com.

"mail.passwall.com" is higher priority for mail servers (50) to send their
e-mail messages, but when unavailable, they can send to
"woodrow.estoremakers.com" (ranked at 100) who acts as a relay to me if
for some reason my host is down. (Different ISP, Different machines - I
can store and forward their mail if/when they are down and they do the
same for me. Also for DNS as we share about 40 domains between us.)

In this way, you can tell your DNS to serve multiple MX records and when
one mail server should no longer be available, the next will be tried by
the remote server attempting delivery. This can work in cases where you
have a transition and an overlap between ISPs or mail servers/IP
assignments.

Is it something to be concerned about? Sure. Even though you have your own
DNS specifying a life-span for information on MX servers, some DNS "out
there" do not respect your settings. 86400 works well for me, but others
like longer times. As you approch the time for your move, you will want to
probably alter your timeout for record information to about a day or
possibly less. This will increase the number of lookups to your DNS as you
migrate, but *should* allow most of those internet DNS to not use a stale
cached copy. Once you cut over, you would want to still use a short time
to make sure all is happy, and when it all appears happy, then extend the
lifespan of the records. ( found some ISP were using old, long outdated
records that were cached for 2-6 months after we moved a web server! Their
DNS did not respect my DNS record lifspan settings. :-/

A majority moved over and respected my settings, but a small group took
longer (10-20%). Of these remaining, about 80% changed after 7 days, and
then the few remaining bad, bad, bad ISPs with their mean, awful, nasty
DNS eventually caught up after a few months.

-ME

-----BEGIN GEEK CODE BLOCK-----
Version: 3.12
GCS/CM$/IT$/LS$/S/O$ !d--(++) !s !a+++(-----) C++$(++++) U++++$(+$) P+$>+++ 
L+++$(++) E W+++$(+) N+ o K w+$>++>+++ O-@ M+$ V-$>- !PS !PE Y+ !PGP
t@-(++) 5+@ X@ R- tv- b++ DI+++ D+ G--@ e+>++>++++ h(++)>+ r*>? z?
------END GEEK CODE BLOCK------
decode: http://www.ebb.org/ungeek/ about: http://www.geekcode.com/geek.html

On Fri, 31 May 2002, Mark K. Kim wrote:
> Not exactly a Linux question, but...
> 
> Our company is trying to change our mail hosting service.  I'm concerned
> we may lose some mail when we suddenly change the DNS (which ultimately
> affects our MX, I think) records.  Is this something I need to be
> concerned about?
> 
> Thanks!
> 
> -Mark
> 
> --
> Mark K. Kim
> http://www.cbreak.org/
> PGP key available upon request.
> 
> _______________________________________________
> vox-tech mailing list
> vox-tech@lists.lugod.org
> http://lists.lugod.org/mailman/listinfo/vox-tech
> 

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