Mailstorm.exe was a utility to send multiple test emails to validate and test Exchange in the 5.5 timeframe, and was used on some of the Microsoft Official Curriculum (MOC) courses.
The utility is no longer used since relied upon a local Outlook install, and my fuzzy brain recalls issues with moving to "current" versions of Outlook such as Office XP.
This is no great loss as it is easy to send test messages natively in Exchange using the Send-MailMessage cmdlet.
Update 30-9-2020: Send-MailMessage is considered obsolete, and has not been updated in a long time.
The documentation provides all the cmdlet details, though the below is typically what I used when running quick tests.
$Creds = Get-Credential
1..10 | ForEach {Send-MailMessage -Subject "Auto Test" -Body "Content Goes Here" -To Local-1@tailspintoys.ca -From user-1@tailspintoys.ca -SmtpServer exch-2010.tailspintoys.ca -Credential $Creds}
Cheers,
Rhoderick