I'm having difficulty dropping unwanted mail that contain chinese characters. I have a content filter that looks for the gb2312 charset but it fails to match properly.

Sample header:
Content-Type: text/html; charset="gb2312"

Filter:
header("Content-type") == "(?i)gb2312"
I run a trace and it does not match and the message gets through.
I have noticed some messages have the Content-type header with a different case like "Content-Type". I tried it both ways and it fails.
Some messsages are chines but do not specify a character set. I typically see somethiong like ?utf-8? in the subject line and that will not match either.