Depending on your mail setup, you might want to simply skip that part that invokes the sendmail executable and use a direct SMTP connection

I think the underlaying send mechanism is SMTP. I only suspect this because I once sent quite a bit of mail through MIME::Lite and got an capacity error sent from the SMTP server. But I don't know for sure.

Setting MIME::Lite to use SMTP with $mime->send('smtp'); was still giving the same tainting error.