Thanks for the help everyone. Does anyone have experience or comments about this:
> The only other solution I can see is to use something > like Nginx to just proxy the SMTP conversation through > the relay to the internal MTA. I haven't tried this before, > but if Nginx can perform fast enough and can also be > DNS load balanced in connecting to internal MTAs, would > it work? If the relay is not near the internal MTAs, will > network latency make this a dubious choice? > > As I understand it, the advantage to that setup would be > that the internal MTAs could be configured as if they were > public facing themselves. Yes?