Not specific to this patch, but I notice that you have in your headers:

In-Reply-To: <y>
References: <y>

This is rather annoying, because it means that anyone else who has the
same lines ends up having their messages attached to your messages as
part of the same thread.

I think you need to read the documentation for git-send-email again -
and check that you're using the arguments concerning message ids and
threading correctly.

Thanks.