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Exchange server failover

Hi all,

I am currently administering a network where we have two separate locations, each with their own exchange server linked via point-to-point T1's. As we are set up, site A is the "gateway" mail server for the domain, hosting mailboxes for users in location A and forwarding messages to the exchange server at location B where those users have their mailboxes located. This works well up until the point where we lose power/internet connection/server crashes in location A. Then no one in location B is able to send/receive email. I was wondering if it's possible to setup location B as a secondary MX for the domain and have it configured to send/receive email for the domain should location A (the primary MX for the domain) become unavailable/crash. Hopefully this isn't too confusing for one of you to help me out with.

Thanks,
Kang
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kangsoh
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kangsoh
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2 Solutions
 
redseatechnologiesCommented:
Hi kangsoh,

If both exchange servers are in the same site - which they must be, then there should be no problem with setting both up to be gateways (so they can both send and receive independantly of each other) and then they will router mail between each other if one should receive mail that is for a user on the other server!

ask a confusing question, get a confusing answer!

Now, that is _mostly_ theoretical, I have done SIMILAR things, but not precisely what you are doing...

Hope that helps,

-red
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SembeeCommented:
I can remove the theory part and say that you can run Exchange in that way as I am doing it for a couple of sites.
Email comes in on either server, once Exchange has got hold of it, it routes it to the correct server. If the correct server is down, then it sits in the queues until it is back up again.

Works very well.

Only note of caution is make sure that you have the same spam filtering on both sites as spammers like to target MX records with a higher value because they often do not have the same level of spam filtering on them.

Simon.
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redseatechnologiesCommented:
Thanks Simon,

I was sure it would work, but hoped you would be around shortly to set us straight either way!

-red
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kangsohAuthor Commented:
Hi guys,

Thanks for the quick replies- I have a couple more questions regarding this topic. In order to implement this solution, do I have to do anything "special" to the exchange servers themselves or will they automatically be aware of what mailboxes are on what server and if they receive mail for mailboxes on the "down" server will they cache it automatically? Also, does this mean that users' emails will get sent out via the "home" exchange server for a user versus a single point on the site, and if this is the case, how should I set up reverse DNS so that the servers wont get mail bounced back at them? Do I just create two reverse DNS entries with 10.0.0.1 pointing to a.mailserver.domain.com and 10.0.0.2 pointing to b.mailserver.domain.com? Finally, does this setup mean that if one server loses their internet connection, outbound email will be routed through the second exchange server on the site that is still connected to the internet? Sorry about the questions, this is the first time I've had to deal with multiple exchange servers on a single AD site and I'm trying to understand everything involved.

Thanks!!!
Kang
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SembeeCommented:
Mailbox information is not held on the Exchange servers, but in the domain. Therefore the Exchange server simply queries the domain to see which machine the mailbox is on and delivers accordingly. Nothing has to be done to Exchange for that to work - other than ensuring that both Exchange servers can see each other.

Reverse DNS settings would need to be created for the Internet IP addresses - not your 10.x.x.x addresses.

However if an Internet connection goes down the server will not use the other server to send the email out. Exchange attempts to deliver the email out through the default gateway configured on the network card, unless specified otherwise through an SMTP Connector.
If you had lost a link and can get to the other server then simply setup and SMTP connector to route the email differently.

Simon.
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kangsohAuthor Commented:
Simon,

Thanks again- I didn't mean to imply that I would use the local IP address for the reverse DNS record, I just put it in to "protect the names of the innocent" as it were. Anyways, thanks for the insight/help.

Kang
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