Thx for your answer, i thought this after reading several subjects.
just can't believe that it's true.

The IronPort cluster is more like configuration cluster, the appliances are sharing the same settings in the cluster but not balancing the load.

If you want load balancing you can do that on DNS level with MX or A records by giving equal weight to both hosts

I have pretty much only worked with hardware-based load balancers because of the need to scale, but there are several lower cost solutions available.

Zeus software has a decent commercial software load balancer:
http://www.zeus.com/products/zxtm/

Here's some information on open source solutions:
http://en.wikipedia.org/wiki/Load_balancing_(computing)
http://www.inlab.de/balance.html

With a pair of C100s I would definitely consider doing it with an open source solution.

DNS round robin MX option is the neatest for sure.

If you add load balancing hardware, then you have to battle issues with the load balancing hardware (ie having two of them so if one fails the other takes over etc).

We had far more issues with hardware load balancing than just straight DNS (which is all we do now).

Hello,

Most mail admins know how to use MX records for load balancing (and redundancy) on their mail servers.
Less people know you can use MX also for your outgoing mail traffic.

Just add a MX record to your local DNS and specify a name for the record. (i.e. outgoingMX.local.domain) put the IP's or hostnames of your internal Ironport card in the data and configure your internal mail system to deliver it’s outgoing mail to smarthost outgoingMX.local.domain
Works for most mail systems. I'm sure it is working for Exchange (5.5. and higher) and Domino (5 and higher)

Regards, Steven

Balancing via MX works well in smaller implementations, but you can't beat a hardware load balancer for bigger environments.

We most frequently see Alteon or Radware boxes in place to handle the L4 magic.