Postbox

Postbox was discontinued in late 2024 when it was acquired by eM Client and all future development ended. There is no native Apple Silicon build — the app runs under Rosetta 2 today but will stop launching entirely when Apple removes Rosetta in macOS 28 (September 2028). With roughly two years until that deadline, you should begin planning a transition now. Postbox's feature set — particularly its Quick Bar, advanced filtering, tabbed workspaces, and unified inbox — made it a power-user favourite, and finding an equivalent replacement will take some research and workflow adjustment. Mozilla Thunderbird is the most direct technical alternative, as Postbox itself was based on Thunderbird's codebase and Thunderbird now ships natively on Apple Silicon with a modern "Supernova" interface. Thunderbird offers advanced filtering, unified inboxes, IMAP label support, and keyboard-centric workflows that appeal to former Postbox users, though some features like the Quick Bar have no direct equivalent. If Thunderbird's feature set does not fully match your workflow, alternatives like eM Client (the company that acquired Postbox), Mailbird (with native Apple Silicon support), or even returning to Apple Mail with supplementary tools like Spark or Hey are possibilities — though none replicate Postbox perfectly. Start exploring alternatives now and plan your migration over the coming months rather than waiting until macOS 28 is released.