Forum notifications get marked by spam filter

[Eugene]

Hi forum admins,
it's rather annoying than problematic but when I receive notification about personal message or any topic that I am watching my spam-filter reports:
X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "MIME-Version"

Indeed in headers we have "Mime-Version: 1.0" two times.

Is it fixable?
Thanks.

[cmb]

That's crafted by SMF I presume, we have the latest stable version. It's open source, if you find a fix let me know.

[Eugene]

In file Subs-post.php, function sendmail().

starting at line 670

				apache_reset_timeout();
		}
	}
	else
--		$mail_result = $mail_result && smtp_mail($to_array, $subject, $message, $send_html ? $headers : "Mime-Version: 1.0" . $line_break . $headers);
++		$mail_result = $mail_result && smtp_mail($to_array, $subject, $message, $headers);

	// Everything go smoothly?
	return $mail_result;

!attention! I did not test it but looks like this is the line causing problem.