Am I blind or is there no way to exclude an account from the unified Inbox?
There’s no built-in option to exclude a specific account from the Unified Inbox view — when you’re in “All Accounts” mode, all accounts are included. The workaround is to use the per-account Inbox views instead: click on an individual account in the left sidebar to see only that account’s inbox. You can also right-click accounts in the sidebar to reorder them. Filtering certain accounts out of the unified view is a reasonable feature request — if you’d like to see it added, filing an issue at GitHub - Foundry376/Mailspring: 💌 A beautiful, fast and fully open source mail client for Mac, Windows and Linux. · GitHub would be the best place to track it.