How do I know what in this inbox actually matters?

You read every line in the inbox. Still you cannot say which message deserves your next hour and which deserves the trash. This is not a flaw in your focus. It is a missing rule. Your team has never agreed, out loud, what matters. So each message gets judged fresh — by mood, by who sent it, by how loud it sounds. That wears you down, and it will keep wearing you down until the rule exists. Make the rule together, not alone in your head. Decide as a group what counts as urgent, what counts as important, and what gets archived without guilt. Then apply the rule like a tool, not a feeling. The inbox stops being a judgment of your worth. It becomes a list you sort.