At the minimum, you will need to declare the encoding for the HTML body part you're sending. See (for example) MIME::Lite for how to specify the encoding of a MIME part of your mail. Also, personally, I wouldn't shell out to sendmail myself but instead I'd use the mail sending facilities of MIME::Lite directly. This also prevents attacks like Shellshock.

As another note, I hope you have sanitized $end_addr, $from_addr and $subject. If for example they contain newlines, your script can easily be abused to send spam.