The option to "archive", "favorite" or organize private messages in your inbox.

I get a lot of messages on a daily basis. Most of them are not worth answering, but still I don't want to delete them for various reasons.

However, the conversations that are worth having get buried in a sea of rubbish -sometime within the time span of only one hour- and are hard to find back.

An option to "favorite" certain conversations, or to "archive" others would solve this issue.