SMTP Stress Testing

[schnazzy1]

Not sure if this is the correct place, but what the hell.
I was wondering if anyone had any suggestions for an SMTP Stress Testing apps?
Currently reading up on Exchange Stress and Performance Tool (ESP) by Microsoft http://www.microsoft.com/exchange/downloads/2000/ESP.asp

Few others I recall but have to read up on include:
MailStorm
JetStress
Avalanche

Any suggestion or direction would be appreciated.

Thanks