December 10, 2025
Inbox wars: Rust vs the relics
Writing an Outlook Add-in in Rust
Rust sneaks into Outlook while devs feud over ancient Windows magic
TLDR: A startup built a Rust add-in to put its tool inside Outlook’s old desktop app, dodging the new web-heavy version. Comments exploded over using AI to handle Windows internals, with many urging code generation or C#, and roasting the new Outlook’s messy web approach—because lawyers live in defaults.
A legal tech startup is sliding its tool, Tritium, straight into lawyers’ inboxes by building an Outlook add‑in—yep, with Rust. Instead of the new web‑heavy Outlook, they’re targeting the old desktop version using Microsoft’s classic plug system called COM (an ancient “Component Object Model”). Cue the comments lighting up like a courtroom drama.
The crowd split fast: one camp cheered the throwback, another rolled their eyes at using an AI text generator (LLM) to figure out tricky Windows interfaces. Meibo dropped a mic on the tech details and then torched the new Outlook as a “JS rats nest.” Others asked: why not just use C# and ship a tiny launcher? The author worried about .NET runtimes, and the thread exploded into a Rust vs C# vs “just use codegen” showdown.
Pragmatists piled on with receipts: ptx insisted the right move is to generate function signatures from the official type library, not hallucinate them. Bri3d flexed, saying they found a sample add‑in in minutes. Meanwhile, jlarocco appeared as the nostalgic parent—“don’t love Windows, but COM is cool”—and pushed code generation as the grown‑up answer.
The vibe: respect for putting Rust in the inbox, heavy side‑eye for relying on AI, and universal dunking on the new Outlook’s web guts. Defaults are the law, but comments are the chaos.
Key Points
- •Tritium is being integrated directly into Microsoft Outlook to fit legal workflows originating from DMS, desktop, and email.
- •The add-in replicates an 'Open with Tritium' entry point via Outlook’s attachment context menu.
- •Legacy Outlook (C++-based desktop) is the current focus; New Outlook relies on WebView and JavaScript for add-ins.
- •Integration uses COM, requiring a DLL that adheres to Windows ABI and calling conventions.
- •Rust implementation leverages the windows-rs crate to implement IDispatch, IDTExtensibility2, and IRibbonExtensibility, using dispatch methods like GetTypeInfoCount, GetIDsOfNames, and Invoke.