In Gmail, type “-in:inbox” or “!in:inbox” in search box and click “Search Mail”,what emails will show up? All emails not in inbox? Not exactly.
You know Gmail delivers conversions instead of emails as search result, so let’s use terminology conversion. Does “-in:inbox” come up with all conversions not in inbox? No, again.
The collection of “-in:inbox” is all conversions not in inbox plus those conversions originated by me or to which I responded.