You're saying this to the wrong person. I run mail systems for a living. IMO, it is a trivial task to send tens of thousands of emails.
What hardware are you running that supports sending out tens of thousands of emails, handling the inevitable DNS errors, timeouts, bounces (yes yes, I've read about the RFC ;)) and that manages all of this in a reasonable amount of time? Genuine question, I'm curious.
If we're only discussing tens of thousands of emails, I'd probably get the cheapest Linode available and bung Exim on it. The average home PC could handle this without issue...
What hardware are you running that supports sending out tens of thousands of emails, handling the inevitable DNS errors, timeouts, bounces (yes yes, I've read about the RFC ;)) and that manages all of this in a reasonable amount of time? Genuine question, I'm curious.