Firstly, in answer to your question, I agree with George_Sherston. Installing Mail::Sendmail seems like the way to go. I don't believe it's a standard module, but it appears to be a pure Perl module, so you should be able to download it from CPAN (see above link), upload it to your home directory, and add something like

use lib "$ENV{HOME}"; 
use Mail::Sendmail;
[download]

to your script (after configuring it).

Secondly, you may not have deserved the severity of the browbeating you received, but you deserved some of it. I don't mean to fan the flames, but surely you must concede that asking a benevolent group of software professionals to help you write code that is truly very dangerous and deleterious to yourself, the Perl community, and the Internet itself. Sure, it may be only for a few users to abuse (before being shutdown), but it comes down to what you were told as a kid by your parents: "What if everyone threw their trash on the ground?" You can see that already there's a lot of insecurity over the web, and fostering one more leak is just out of the question. I think that merlyn thought that you were knowingly writing this hole to abuse yourself, though it appears to me that this is not true, though I can certainly see why he thought that (I did too until I read this post). Realize it was not necessarily the content of the code that was being attacked, it was the security.

This is the best I can do and would prefer not being mocked.
If you open yourself to suggestion (but not attack) from others, this doesn't have to be so. "Experience is a dear teacher, but fools will learn at no other." - Poor Richard's Almanac

(Ok, so I stole that from The Mythical Man-Month ;) )

Update: upon inspecting this, I don't think I made my own gut reaction to this code clear. I second merlyn's sentiment: Please do not deploy this code. It's great that you learned from writing real-world code, it really is, but this is not an Internet-ready email application, and shouldn't be deployed as one.