Default [Q] Convert SMS to MMS at Will?

For host alerts at my place of work we use Nagios to send email alerts to the email associated with our phone number by the carrier so if your phone number was 555-555-1234 you could send an email to your phone with:

SMTP:5555551234@messaging.sprintpcs.com

These come through as an email address and with I believe the stock app and Handcent I can reply to these the four digit code associated with an alert to acknowledge them and sort of take responsibility for fixing the issue. I was kind of wondering why only some apps support this and how some of them just fail to send. I was also kind of hoping there was a way to make all sms applications support this. I believe the apps that support it are converting from sms to mms because the target is an email. Which brings me to my apology if this is already a thread somewhere. It's incredibly difficult to search using the same keywords someone would use to do the opposite of what you're looking for. If a solution for this exists I'm sorry. Anytime I search for a solution to this I get "how to stop sms converting to mms" and many other similarly titled threads. Any ideas?