Why GMail doesn't have filter for unreplied mails?

They do: it's your inbox. Once you reply, you archive the e-mail.

The problem is I never archive the e-mail and I'm looking for simple is:unreplied.

So what would happen with all the e-mail you get that doesn't require a reply?

(This is where the strength of Archive comes in)

You can create a filter that marks any mail containing "Re:" with a specific label (lets say Reply), and the search for -{label:Reply}

alternatively, skip the labeling part and search for -{"re:"}

Thanks, works!

Can't you just do a quick search with "label:unread" in the search box? That's what I have been using to filter unread message. Not as convenient as a dedicated button, but still does the job !

I wonder if there might an operator for number of messages in a 'conversation'.