Email redirection  MX perference = 10, mail exchanger =  MX perference = 20, mail exchanger =

Independent Mail server (Exchange 2007) (Linux postfix server)

Supposed some unknown email or MAIL1 email service down. Based on MX record, those email will be auto tried to send to MAIL2 server.  The both server have their own user accounts, so those email are also rejected by MAIL2 server.
As I know, some ISP will have some services to hold those unreceived email, and then send back to clients when MAIL1 service is normally restarted

1. Can I set MAIL2 for temporary pick up all MAIL1 incoming email when MAIL1 is down, same as ISP service? Is it possible (MAIL1 = Exchange / MAIL2 = Linux)  or (MAIL1 &  MAIL2 are both running Exchange) ? If worked, what I need to prepare?

2. If not, how can I prevent all MAIL1 unacceptable email redirect to MAIL2?

Thanks !
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i don't think that will work if you have to different mail server apps and OS's. If you have two Hub Transport Servers for Exchange then you could set up an NLB that would provide redunancy.

if you want mail2 to take over you chould change the NAT'ing on your firewallso that mail1 record points to mail2, but obviously this is a manual step.

You could potentially use a DNS round robin to point at the two server but that might interfere with normal mail flow when both are available. You would need to separate those from client access dns records i.e. OWA.

To do this you would need to set up the shared namespace (i.e. non authoritative for the domain name)  on exchange 2007 so the two servers bounce the mail between them.
you can do this by setting up a catchall for that domain or server 2.
then distribute the mails using pop or whatever to server1

to prevent the mail being rerouted, just remove the mx
On my network, we have our primary Exchange 2010 server which handles all user mailboxes. We also have a Linux VPS which hosts all our websites and is configured to be the backup MX.

For each Internet domain we have public DNS records something like " IN MX 10" and " IN MX 20". That means any time someone wants to send us email, they will try the lowest valued MX first (i.e., and if that can't be contacted, they'll try the VPS.

The VPS is then configured as a "remote" mail exchanger (terminology depends which Linux mail daemon you plan to use) but basically it's configured so that it will accept mail for the particular domain, but it also knows the domain is not hosted locally. If it receives an email for that domain it will continually try to deliver it to the lowest DNS record being our Exchange server.

Any mail server software should be capable of this setup (especially where Exchange or Linux is envolved), it's just a case of setting it up.
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In our network, we have 3 Linux Postfix servers that has the MX role. Our Exchangeservers are not in the MX records.

The transportrules on the Postfixservers are set to route mail to the accepted domains on the different Exchange servers.

If one of the Exchangeservers is down, the Linuxservers cache the mail until the Exchange is up again. Then the cached mail will be delivered to the Exchange.

We want to separate the MX from the Exchange, and our solution works great for us.
rhinocerosAuthor Commented:
Thanks everyone !

>>to prevent the mail being rerouted, just remove the mx (Exchange 2007) (Linux postfix server)
Independent Mail server, they have their jobs and different accunts....
e.g  MX perference = 10, mail exchanger =  MX perference = 20, mail exchanger =
In my opinion, mx record is to redirect email to a mail host. Except reroute problem, so the above mx reocrd setting is wrong? If true, what I need to change ?

I will get more info about VPS.

>>Our Exchangeservers are not in the MX records.
Mx record is to redirect email to a mail host. No MX is also worked?
That's correct. MX points only to the Linux servers. Postfix sends the mail to the Exchangeservers (after SPAM checks etc) via the transport config in Postfix.

For example if we had a domain called The MX for that domain points to one of our Linux Postfix servers. In the transport config on the Postfix server, it says that domain is going to be sent to That Exchangeserver has domain in its accepted domain list. This config lessens the burden on the Exchangeservers, since all SPAM/viruschecks happens on the Linuxservers.

No need for the MX to point directly to an Exchange.
rhinocerosAuthor Commented:
Any further idea please? Thanks !
i can suggest an external spam provider that does proper caching of the mail so that it will hold it all for you
As @irweazelwallis suggested, you could use an external spam filtering provider. That way the public Internet never knows the public IP of your Exchange server (you could configure port 25 to only accept email from your spam provider) and it would avoid the necessity of managing your own backup MX with the added benefit of spam filtering. They would filter any spam/viruses etc, then forward the mail to your Exchange server. In the event the Exchange server is not available (e.g. network outage or hardware failure), they will cache all your email for a period of time until the server is back up and running.

I've been using a Barracuda Spam Firewall appliance on my network for the past 3yrs and it's been excellent. Barracuda also have a cloud filtering product which might be suitable in your case. They will cache your email for up to 96 hours if your local server is unavailable.

McAfee have a SaaS inbound filtering product with various subscription options. The SaaS Inbound Filtering product would be suitable for you.

Webroot gave us a demo of their SaaS filtering service and it also looked quite capable of doing the job.

There are plenty of other providers around. Those are just the few that I've had direct dealings with and would recommend off the top of my head.
Webroot is one i have used. they will be able to cache I think up to 7 days of emails
That would be the easiest method of trying to cache you emails if one server is offline
rhinocerosAuthor Commented:
Although I did not get the finally answer, thanks everyone!
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