I don't think you can tweak gmail's spam filter. Not directly, anyway.
On 12/19/09, Tim <ignored_mailbox yahoo com au
> On Sat, 2009-12-19 at 00:14 -0500, Marcel Rieux wrote:
>> All your messages at gmail end up in my spam folder with the following
>> Warning: This message may not be from whom it claims to be. Beware of
>> following any links in it or of providing the sender with any personal
>> information. Learn more
> A different Tim, here, but that might be due to him posting through the
> gmane usenet to email gateway (it gives me problems, too; different
> problems, though). You could have a look through the headers of one of
> his mails, and see if there's something in there you can use to tell
> your mail filter that those messages aren't spam.