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Redundant mail path for Exchange 2003

Posted on 2009-07-08
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Last Modified: 2015-01-05
Hi, we have 2 x offices connected via WAN. Each office has its own internet connection (separate to our WAN connection), but all email comes into office 1. The exchange server here then passes emails to the server in office 2.


The internet in office 1 was down all of yesterday, which made me think, is there a way we can redirect our email (ingoing / outgoing) through our office 2 server?

My understanding of it is we can add another SMTP connector to both servers with a higher cost, so exchange will fall back to the secondary connection if it needs to.

We only have 1 server per site, so I'm not sure about this front end / back end / bridgehead arrangement. But I am also curious to know if mail starts coming in through exchange server 2, will it know to automatically send mail up to exchange server 1? (as it has never had to do this before, usually its the other way around)


My thinking may be way out here, hope someone can help out!
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Question by:dekkar
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Accepted Solution

by:
dnilson earned 168 total points
ID: 24810516
Configure a MTA connection between the two servers, setup the DNS to use both SMTP servers using mx records and wail away!
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Assisted Solution

by:Dave Howe
Dave Howe earned 166 total points
ID: 24811257
if they are both part of the same email domain, then yes, it will pass the message correctly to whichever server has the mailstore for that user.

and yes, adding a second bridgehead (with higher cost) to the second office will allow fallback to that if the primary bridgehead is unavailable - it may not fail back automatically though, as in exchange's opinion, the bridgehead is "up" - its all the rest of the internet that is down :(

getting inbound routing is simple - just add a second MX record to your dns (with a higher value than the primary) pointing at the internet NAT address for the second bridgehead.
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Assisted Solution

by:Mestha
Mestha earned 166 total points
ID: 24812085
Sorry to say, but adding another SMTP connector with a higher cost will NOT give you redundancy.
If the primary connection is not available, Exchange will not try the higher cost connector. It will simply queue the email.

Exchange matches the address space, if there are two connectors with * but different costs then the lowest cost will always be used and the higher cost ignored. Costs are designed for use with specific domains, so you would have example.com with a cost of 1 and * with a cost of 2, then email for example.com would go out the first connector and then everything else out the second connector.

The most that you can do is load balancing, with two connectors of a cost of 1, or two bridgeheads set in the same connector.

With regards to inbound email, as far as I am concerned, all MX records are equal. Furthermore if you do set a second connector with a higher value, then it will receive more spam than the lower cost. Therefore if you are going to have both servers exposed to the internet then you need to ensure that both servers have the same Antispam and Antivirus solution installed. They need to be configured identically, so recipient filtering etc enabled.

Simon.
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Expert Comment

by:Dave Howe
ID: 24813176
Mestha: yep, my point exactly. however, you can run a scheduled job to ping a remote IP, and shut down or start up the service as appropriate.
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Expert Comment

by:Mestha
ID: 24814088
Start what service?
There is no way to control the routing in Exchange depending on whether something is down or not. You cannot stop SMTP because that will affect inter-server traffic as well.

If there are multiple sites then another way round it is to use a smart host that is under your control. That is what I do with a number of clients. Doesn't matter where the email originates from, it all leaves via a single host on the internet (actually a cluster of machines, but it is a single "host" name).

Simon.
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Expert Comment

by:Dave Howe
ID: 24814299
Mestha: on the script I use, it uses Set-SendConnector with the -enabled parameter to shut down the bridgehead unless it can successfully ping the upstream router at the ISP.
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Expert Comment

by:Mestha
ID: 24814512
This is a question about Exchange 2003. So Powershell doesn't apply.

Simon.
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Expert Comment

by:Dave Howe
ID: 24815714
hmm. I didn't think exchange 2003 used smtp for links between servers, I thought it used rpc?
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LVL 65

Expert Comment

by:Mestha
ID: 24815907
Inter-server traffic goes over SMTP. That has been the case since Exchange 2000. That is why you will see in all the migration questions the first thing that is asked is about SMTP connectivity.
Stop SMTP and no traffic will flow between them. Try it and see.

Simon.
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LVL 11

Author Comment

by:dekkar
ID: 24836084
Hi... Thanks for the replies... It does shed some light on inbound, which is pretty straight forward. Outbound however seems to be impossible to have redundancy?

Does Exch 2007 provide this? As it could be the excuse I'm looking for to upgrade!


Thanks,
Dekkar
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LVL 65

Expert Comment

by:Mestha
ID: 24836499
The behaviour hasn't changed. All it does is load balance, nothing else.

Simon.
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Author Closing Comment

by:dekkar
ID: 31601387
working.
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