When we become not relavant to a subject of discussion in huge mail thread (with say 100 or more people), we would like to opt-out.
In such case, it is not easy to tell every one to remove us from the thread. next immediate replying person can remove. but some one might reply on top of old mail which again brings us back in to loop.
Mail client like Microsoft Exchange or gMail shall provide "opt-out" option.
On choosing this, mail client like outlook shall handle removal : similar to the way outlook meeting participants are handled.