Maria mentioned risk in her response. The very first task you need to do is to identify any key business processes or rules that may be impacted by such an architectural change.
For example, are there any e-mail archiving tools that may be impacted by such a change? Anti-virus software? workflow based applications? What happens if the smtp service goes down on one of the clustered boxes? Is there any impact of your applications now having to route through a mail server instead of directly to a SMTP box? etc etc.
We run smtp on our mailservers with no problem.We have other servers that drop mail to them via smtp.
But we also have a mail gateway for internet mail. That’s where my concern would come in. If you’re talking about making the user’s mailserver connect directly to the internet…there are a lot of issues there. What if the virus scanning software (you are running some?) goes awry? What if spam backs up over some weekend and dumps the server? You put the user environment more at risk when you don’t have a mail gateway.
I’m not saying it can’t be done, just that the risks should be considered against the possible benefits.
You might consider using a product like VMWare to run multiple Domino “servers” on each of the boxes listed above. This would keep the internet mail gateway separate from your user environment.