postfix help, please

[Lisa Kachold]

Hi David!

On 7/29/09, David <david at damnetwork.net> wrote:
> We are currently running postfix as our edge relay server.   All email is
> currently forwarded to an internal Notes server.
> We are also in the process of migrating to exchange.   I have no problems
> with getting the mail to exchange, however, the powers that be want all
> incoming mail to be delivered to both the new exchange server and the old
> Notes server.
>
> Basically
>
>                            -> joe.user at domain.com (exchange server)
> in -> joe.user at domain.com -
>                            -> joe.user at domain.com (Notes server)
>
> I have 2 issues.   If I specify exchange.domain.com and notes.exchange.com
> will the "to" address be re-written?
>
> Also, How the heck can I do this?  The closest I could find was:
>
> http://www.lslnet.com/linux/edosc/52/linux-52354232.htm
>
> but the translation isn't perfect, and I believe some of the characters
> aren't getting displayed correctly.   Mainly, this regex:
>
> /^ (. +) $ 1 at backend1.x-si.orgx-si\.org$/ $ 1 at backend2.x-si.org

> Any help would be appreciated.
>
> David

This can be done trivially via DNS MX record round robin heirarchy.
Simply configure equal priority MX records for both servers:

In order to utilize the Roller Network mail services, the DNS records
for the domain name must include proper MX records. Depending on the
service used (Secondary MX, SMTP Redirection, etc.), different MX
priorities are utilized. Some accounts are eligible for advanced or
dedicated servers; a full list of available SMTP servers is shown on
the Resource Access page.

Equal priority MX records for the Roller Network mail servers should
be used. Not only does this distribute load across our incoming paths,
it also prevents false rejection scanner errors. (We have internal
hardware load balancers to handle redundancy internally.) Equal
priority MX records still roll over to others of the same priority if
one is unavailable.

Example -  Secondary MX:

example.com IN MX 0 yourMTAserver.example.com
example.com IN MX 5 mail.example.com
example.com IN MX 5 mail2.example.com

Example - (SMTP Redirection, Hosted Mail Domain):

example.com IN MX 0 mail.example.com
example.com IN MX 0 mail2.example.com

caution If your current DNS provider is unable or unwilling to add
equal priority MX I recommend moving your DNS to a provider that
allows proper MX records to be configured

DNS Round robin (random load balancing) looks like this:

www0 IN A 1.2.3.1
www1 IN A 1.2.3.2
www2 IN A 1.2.3.3
www3 IN A 1.2.3.4
www4 IN A 1.2.3.5
www5 IN A 1.2.3.6

www IN CNAME www0.foo.com.
www IN CNAME www1.foo.com.
www IN CNAME www2.foo.com.
www IN CNAME www3.foo.com.
www IN CNAME www4.foo.com.
www IN CNAME www5.foo.com.

Notice that this seems wrong, but is actually an intended feature of
BIND and can be used in this way. However, now when www.example.com
gets resolved, BIND gives out www0-www6 - but in a slightly
permutated/rotated order every time. This way the clients are spread
over the various servers. But notice that this not a perfect load
balancing scheme, because DNS resolve information gets cached by the
other nameservers on the net, so once a client has resolved
www.example.com to a particular wwwN.example.com, all subsequent
requests also go to this particular name wwwN.example.com. But the
final result is ok, because the total sum of the requests are really
spread over the various webservers.

http://forums.devshed.com/dns-36/mx-load-balancing-using-round-robin-method-75775.html

Other suggestions include:

1) OpenExchange
2) Toaster shared mail NFS drives to multiple servers.

I would not ever in a thousand years move away from a linux MTA
running clamd, spamassassin for Exchange.  I would set up external
mail to Linux with a well configured firewall, and a null mail relay
to OpenExchange for internal mail.

Call me if you want a consultation for the powers that be?

> --
> "I find your lack of faith disturbing."
> --Darth Vader
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