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Does Outlook Web PWA Store an OST File Locally?

Maira Mehtab Sep 20, 2026 868 views

Question details

The user is inquiring whether the Outlook Progressive Web App (PWA) or Outlook on the web creates and stores a large local OST mailbox database file on their computer.

Product: Outlook Web PWA
Device & OS: not provided
Scenario: Determining local storage requirements and data security implications when deploying Outlook on the web instead of the traditional desktop client.
Observed behavior: Outlook on the web and the Outlook PWA do not create or use a large desktop OST mailbox database; they only retain limited browser cache, cookies, and local settings.

Before you start

Verify your organization's data retention and privacy policies to determine if storing limited browser cache and cookies locally is acceptable for your security standards.

Solution 1Recommended

Utilize Outlook Web or PWA to Prevent Local OST Generation

Transitioning users to Outlook on the web or its PWA is an effective way to avoid dealing with bulky local OST files, keeping the vast majority of mailbox data strictly in the cloud.

Unlike the traditional Outlook desktop application, the web and PWA versions do not download an entire Offline Outlook Data File (OST).

This significantly reduces local disk space usage and minimizes the risk of local data corruption, as the application relies on cloud storage for active email browsing.

Access Outlook on the web

Open a modern web browser and navigate to the official Outlook on the web login portal.

Install the Progressive Web App (PWA)

Click the 'App available' or 'Install' icon located on the right side of the browser's address bar to install Outlook as a lightweight desktop window.

Manage local settings

Configure local preferences within the PWA, noting that only minor interface settings and a small cache are saved to the local hard drive.

Storage Limitation: While no OST file is created, be aware that the browser or PWA will still store a small amount of necessary cache and cookies to ensure the application loads efficiently.

Solution 2

Clear Browser Cache to Eliminate Local Data

If strict security policies dictate that absolutely no local data should remain on the machine, you must clear the browser's cache and cookies.

Free Microsoft Office alternative

Switch to a Lightweight and Highly Compatible Office Suite

If you are moving away from heavy desktop applications like traditional Microsoft Outlook and Office to save space, consider WPS Office. It provides a lightweight, highly compatible alternative for Word, Excel, and PowerPoint files without burdening your local storage.

1. Download the installer: Visit the official WPS Office website and download the free version optimized for your operating system.
2. Install the application: Run the installer file and follow the straightforward on-screen prompts to complete the setup.
3. Open and edit files: Launch WPS Office to easily open, edit, and save your existing Microsoft Office documents without bloated storage files.

Lightweight installation prevents unnecessary local storage consumptionHighly compatible with Microsoft Office formats including DOCX, XLSX, and PPTXBuilt-in cloud syncing for secure and easy document access across devicesFamiliar user interface makes transitioning completely effortless

microsoft office alternative - wps office

Frequently Asked Questions

Can I view my emails offline using the Outlook Web PWA?

Outlook on the web and the PWA offer very limited offline capabilities. Because they do not store a complete local OST file, you cannot browse your entire historical mailbox without an active internet connection.

Does removing the Outlook PWA delete my emails?

No. Your emails, contacts, and calendar events remain safely stored on the Microsoft cloud servers. Uninstalling the PWA only removes the application shortcut and local cache from your device.

How large is the local cache stored by the Outlook PWA?

The local cache is generally very small, typically ranging from a few megabytes to a couple of hundred megabytes. This is significantly smaller than a traditional desktop OST file, which can easily grow to tens of gigabytes over time.

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