Currently it's not possible to follow a bug, aka getting all replies by mail, without writing a reply.
I have not tested it if making a reply can do it.
Even when it works, it would make the replies unusable, because when eg. 100 persons would like to follow all would need to write a reply.
Also it could be done for complete projects.
I might add a follow command then for projects and bugs. This shouldn't
be hard to implement.
The two typical mailing list functions would IMHO suffice: subscribe and unsubscribe