The Outlook mobile app caches emails, attachments, and calendar data so your inbox loads instantly, and that cache plus downloaded attachments can quietly use a gigabyte or more. On Android you clear it in Settings; on iPhone you offload or reinstall.

Short answer:

  • Android: Settings > Apps > Outlook > Storage & cache > Clear cache (safe; keeps accounts signed in).
  • In-app (both platforms): Settings > tap your account > Reset account to re-sync and clear local cache.
  • iPhone: Settings > General > iPhone Storage > Outlook > Offload App, or reinstall.
  • Avoid Clear storage / Clear data, which removes your added accounts.

Why Outlook's Storage Grows

Outlook caches a local copy of your recent emails, attachments, contacts, and calendar so the app feels fast and works offline. Every PDF, image, and document you open gets cached, and over months this builds up, especially across multiple connected accounts.

Because your real mail lives on the server (Exchange, Microsoft 365, Gmail, etc.), the local cache is fully rebuildable. Clearing it does not delete a single email from your account; the app just re-downloads what it needs. The only thing you lose by clearing cache is the offline copy until it re-syncs.

Clear the Outlook Cache on Android

Android's storage screen is the cleanest fix on a phone.

  1. Open Settings > Apps.
  2. Scroll to and tap Outlook.
  3. Tap Storage & cache.
  4. Tap Clear cache.

Your accounts stay connected and the freed space registers immediately. This also clears up many sync hiccups and stuck attachments.

Important: the same screen has Clear storage (or Clear data). That resets Outlook to a fresh install, removing every account you have added and all local settings, so you would re-add and re-authenticate each mailbox. Use it only if Outlook is broken. The clear cache vs clear data guide explains exactly what each button removes, and how to clear app cache on Android safely covers the routine.

Reset an Account to Clear Local Data (Both Platforms)

Inside Outlook itself, you can clear an account's local cache without uninstalling, which works the same on Android and iPhone.

  1. Tap your profile icon (top-left), then the gear / Settings.
  2. Tap the email account you want to reset.
  3. Scroll down and tap Reset account.

Outlook clears that account's local cache and re-syncs from the server. Your emails reappear, but the bloated offline copy is rebuilt fresh and smaller.

Clear Outlook Storage on iPhone (Clenoir)

iOS has no per-app cache button, so use these:

  • Offload App: Go to Settings > General > iPhone Storage > Outlook and tap Offload App to remove the app and cache while keeping its data, then reinstall.
  • Delete and reinstall: For a full purge, delete Outlook and reinstall it from the App Store, then re-add your accounts.

To see how much space Outlook and other apps actually use on iPhone, a Clenoir storage scan lists them clearly and lets you confirm each cleanup before anything is deleted.

Trim Attachments and Keep Outlook Lean

Attachments are often the hidden weight inside the cache.

  • Lower the sync window if available so Outlook keeps fewer days of mail cached offline.
  • Avoid opening huge attachments repeatedly on mobile; download them once and delete from the device.
  • Reset the account or clear cache every couple of months if your mailbox is busy.

Outlook is rarely the largest app on a phone, so if storage is still tight, photos and video are the usual cause. For a wider cleanup, see the clean up phone storage hub and the storage cleanup FAQ, which point you to the categories that actually move the needle. Clearing Outlook's cache is safe, quick, and never touches the emails on your server.

FAQ

How do I clear the Outlook cache on Android?

Open Settings > Apps, tap Outlook, tap Storage & cache, then tap Clear cache. Your accounts stay connected and the freed space registers immediately, which also clears up many sync hiccups and stuck attachments.

Will clearing the Outlook cache delete my emails?

No. Your real mail lives on the server, so the local cache is fully rebuildable and clearing it does not delete a single email. The only thing you lose is the offline copy until the app re-syncs.

How do I reset an Outlook account to clear its local data?

Tap your profile icon (top-left), then the gear / Settings, tap the email account you want to reset, scroll down, and tap Reset account. Outlook clears that account's local cache and re-syncs from the server, rebuilding a fresh, smaller offline copy.