Re: IIS SMTP server in a redundant formation?

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On 3/10/2009 7:37 AM, kammy_boy186@xxxxxxxxxxxxx wrote:
We are looking to build a new Windows 2008 relay and I was looking at some sort of redundancy in case we lost this box (called Relay2). The idea was to build two similar servers, Relay2 and Relay3, and create an MX record named Relay.

I don't think that relying on multiple (equal cost) MX records will actually do what you are wanting to do, or if it does, it will do so very poorly.

Relay would point to Relay2 and Relay3 (both will equal cost).

Are you really wanting your Relay(1) to send to either Relay2 or Relay3? Or did you mean for the AppServer to send email to either Relay2 or Relay3, thus supplanting Relay(1)? (The latter is how I have taken your question.)

This way, if we lost either box, we would not lose the messaging functionality.

*nod*

Though I admire what (I think) you are trying to accomplish, I don't think it will work out quite the way that you are wanting.

First, SMTP server will usually cache the result of an MX record lookup and continue to use it until it is unable to do so (server being down). At first this may seem ok, but if you want to try to spread load across multiple MX servers, you will find that connections tend to find an MX server and stick there. The same also applies to a DNS record resolving to multiple IPs, if not even more so.

Second (and based on my understanding of your question) I don't think that your AppServer's applications will be doing doing MX lookups to decide what server to connect to. Thus, if the server that a given application is to connect to is down, it will not be able to send email.

What I would recommend is that you look at something like Network Load Balancing between Relay2 and Relay3 and then have your applications connect to this ""virtual server that is comprised of Relay2 and Relay3. This way your back end applications will have some redundancy.



Grant. . . .
.

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