2 ISP connections to single Exchange 2003 server

Posted on 2009-02-19
Last Modified: 2012-05-06
I was reading this Experts Exchange discussion, but it seem to stop without a solution.

We are changing our ISP over which we send/receive email.  During the DNS propagation time I would like to receive via our other ISP, but still send email originating in our office out the new ISP SMTP server.  I figured all I needed to do was set up a second MX record.

But in testing if I telnet second_ip_address 25 from outside I get no response.  Doing this internally within the lan works fine.  

Can I get it to respond to email from both routers?  I could just change the default gateway for a couple of days, if necessary, but I would like it for failover purposes.

Question by:holeejo
    1 Comment
    LVL 65

    Accepted Solution

    The default gateway is the key here.
    You can only have one default gateway for the traffic to go back out through.
    You would need to have a second machine for both gateways to be active, so the email can be delivered in to either server.

    What I do for ISP change is use a dynamic DNS account. The dynamic DNS host is added to the MX records at least 48 hours before I make the change, so that it is fully propagated. Then when it comes to the switch over, I simply change the dynamic DNS IP address. That change is live in a few minutes. The real DNS record can then be changed. You are without email for a few minutes at most.


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