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Legacy Feature	Availability in Web Add-in	Reason for Removal
Automatic categorisation of saved e-mails (“Saved” purple category)	Supported in clients supporting Mailbox API v1.8+, list of supported clients - https://learn.microsoft.com/en-us/javascript/api/requirement-sets/outlook/outlook-api-requirement-sets?view=common-js-preview&tabs=jsonmanifest#outlook-client-support
Real-time monitoring of incoming e-mails (background operation)	Not supported	Modern add-ins execute only when the task-pane is open; global “all-items” events aren’t exposed.
Processing while Outlook is minimised (VSTO background thread)	Not supported	Office JS code stops once the pane closes; persistent background threads are disallowed.
Automatic display / persistent pinning of the add-in pane	Partially supported — user must open the pane; *Pin* works only in Windows desktop Outlook, not in Outlook on the web	Office JS cannot programmatically open or pin the pane; OWA currently lacks a pinning feature.
MSI installer / GPO push deployment	Replaced — install via Microsoft 365 admin center → Settings → Integrated Apps or per-user sideloading	Modern add-ins are manifest-based web apps; Microsoft has deprecated MSI + GPO deployment for Outlook add-ins.
Bulk / silent configuration for multiple users (registry or script)	Not supported	Office JS settings are stored per mailbox and must be set interactively; no bulk-write API is available yet.
Registry-based silent configuration	Replaced with interactive Settings UI	Web add-ins cannot read Windows Registry; settings must live in roaming storage.
Direct opening of cases in Patricia Desktop	Not supported	Office JS cannot access local desktop apps.
Support for Outlook 2007 / 2010 / 2013	Dropped	Microsoft allows modern add-ins only on Outlook 2016 (build 16.0.9126) and newer.
Direct COM access to Outlook object model	Not supported	COM interop is unavailable in Office JS; only the subset exposed by Office JS can be used.
Local log file `DocIntegrateOutlook.log`	Replaced with in-pane diagnostics	Browser sandbox prevents writing to the local file system; diagnostics surface inside the pane.
Support for non-HTTPS DMS endpoints	Dropped — HTTPS required	Office JS blocks insecure HTTP requests inside Outlook; mixed content is disallowed.

What this means for users

The add-in pane is not shown automatically. In specific versions of Outlook for Windows you can open it once and press *Pin* to keep it docked; in Outlook on the web and new versions of Outlook you must open it manually every time.
The add-in processes e-mails only while its pane is open. Switch away and processing pauses.
Installation for multiple users goes through *Microsoft 365 admin center → Integrated Apps* (or each user can install individually); MSI + GPO deployment is no longer supported.
Each user must configure their own DMS connection (gear-icon *Settings*); bulk pre-loading is not available today.
Opening of cases in Patricia Desktop is not supported anymore
The DMS URL must start with https:// — plain http:// endpoints are rejected.
Outlook ≤ 2013 is no longer supported. Those users should stay on the legacy add-in or upgrade Outlook.

Rationale

Security — modern add-ins run in a sandbox: no COM, Registry, file-system access, or insecure HTTP traffic.
Governance — Microsoft has deprecated MSI / GPO deployment; admin-center installation and manifest sideloading are the supported paths.
Cross-platform — one code-base for Windows, Mac, Web, and Mobile required dropping Windows-only hooks and direct desktop launches.

We will continue to watch the Office JS and Microsoft Graph roadmaps and re-introduce any of the above features if the necessary APIs become available.