Running a second "emergency" mail server in an exchange environment.

I am looking at ways of minimising end user down time in the event of my Exchange 2003 server failing. I am running exchange 2003 enterprise in a single domain with 70 users running outlook 2003. My ISP is demon internet and the email comes to my exchange via SMTP and I send using the demon smart host. If exchange is offline Demon have relay servers that keep trying to send the mail  I do not have the option to access this stored mail via a pop account.

The scenario I want to protect against is motherboard/power supply failure - i.e. something that could render the server unoperational for up to 24 hours but would not affect the hard drives so that as soon as it comes back on line exchange will come back to life.

What I need is something that can act as a stop gap during this period. I have a rough idea of what I would like to happen but would be grateful if somebody answer my queries, point out any flaws or suggest any other ideas.

Firstly, i intend to make sure all users have cached exchange mode enabled in outlook so that all users have access to their mail folders if the server goes offline.

Next I would like to have a second mail server preconfigured on my network - something like hmailserver or xmailserver.  If the exchange server goes down I can then quickly reconfigure the firewall so that all incoming mail is diverted to the backup server. Users can then get their email  either via another client (outlook express or whatever webmail clients the backup mail sever offers) or directly into outlook if possible.

Then once the exchange server is repaired I can change the setting back on the firewall and everybody starts using exchange again.

Can anybody let me know whether my plan is feasible? Can 2 mail servers co-exist on the same domain without fighting with each other?

The area I am really not sure about is how the users will get their email. Is it possible for them to configure outlook to connect to another mail server, download email into their offline mailbox and then when exchange comes back on line have this mail resynched with their exchange mailbox?

Finally, does anybody have any comments of either of the two mailboxes I have mentioned to could suggest any others?
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ryansotoConnect With a Mentor Commented:
Ok let me try and explain -

You have one mail server with all the mailboxes on it, thats fine.

Lets say you set up server 2 - which is completely fine in an exchange environment.  Messaging will work fine.

OK so on server 1 you have all your users and boom mobo dies.  No one will have access to their mailboxes regardless if you have 2 or 200 hunred servers.  If the server that contains the mailboxes dies all mailboxes on it will not be accessible.

Now with multiple servers the idea is to create a front end/back end scenario.

1 front end server that you point the firewall to.  Multiple backend servers that contain all the mailboxes.
The reason for this besides just 2 mailservers is OWA.

with just 2 mailservers you run into issues with exchange.  If goes to your exchange server 1 then only those mailboxes will be accessible from the outside.

If I were you I would go one of 2 ways
1.  Cluster
2.  Front end server then a couple backend boxes

If you want 100% reliablility then a cluster is probably your best bet.  Server 1 dies server 2 kicks in and no changes needed.
tigermattConnect With a Mentor Commented:
I would avoid trying to run two different mail server packages on the same network. I can foresee you getting yourselves into complications with creating email addresses on both servers and all sorts of other administrative issues.

The usual methods for ensuring high availability of Exchange environments are to either use a Windows Cluster or invest in a 3rd-party replication and failover solution. The first option - a cluster - can be very expensive; you must have Windows Server 2003 Enterprise Edition, and Exchange Enterprise Edition for it to support clustering. With the latter, a solution like DoubleTake is still expensive, but maybe not as expensive.

With Doubletake, you would still need two servers, and two licenses for the server OS and Exchange. However, Doubletake can then be configured to perform the replication and AUTOMATED failover if one Exchange Server fails, almost seemlessly to your users. It is a brilliant solution for smaller companies (compared with the sort of companies who actually use clustering, probably less than a few thousand users) who need redundancy for their mail service but don't want the hassle or expensive of Exchange clusters.

metamaticAuthor Commented:
many thanks
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