There's a potential spam issue, because your error checking is poor. However, since you don't provide a sample template, I can't be sure.

Your code:

defined $from && $from =~ m/.+\@.+/
[download]

doesn't forbid a newline. If that newline is inserted into the header of the message, a spammer can create an arbitrary subject and sender, and then a blank line, permitting an arbitrary body. Sure, your added header and sender will be at the bottom of the message, but at that point, who cares?

Also, just being able to send a message to a recipient designated by a form field is considered very bad manners in this day and age. Please discontinue the promotion of your mailscript.

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