How can I make my reply to be linked within a mail thread?

[Terry Guo <flameroc@xxxxxxxxx>]

Hello,

Suppose I didn't subscribe gcc mail list, and I want to share my
comments for an existing mail thread after I read it in the mail list
webpage, what should I do to make sure my reply can be linked into
this thread? It seems that composing a mail with subject like "Re:
ORIGINAL-SUBJECT" and then sending it to mail list doesn't work.  My
email at http://gcc.gnu.org/ml/gcc-patches/2012-03/msg01763.html
doesn't get linked to expected mail thread at
http://gcc.gnu.org/ml/gcc-patches/2012-03/msg00461.html.

Please advise, thanks in advance.

BR,
Terry