Shrinking Your Outlook Cache File

Shrinking Your Outlook Cache File

If you receive a message like this in the Outlook App:

This is usually due to the size of your email files. We don't see it too often anymore because outlook uses cloud storage for most things, and only caches things locally as needed, but you may have set your Outlook cache to be for a really long time, so if we reduce this amount, your outlook file should shrink down. The maximum size out of the box is 50 GB.

đź›  Step-by-Step Instructions
  1. Open Outlook.
  2. Click on File (top left corner).
  3. Choose Account Settings âž” then click Account Settings again from the dropdown.
  4. In the Email tab:
  5. Click on your email account (it should say “Microsoft Exchange” or "Office 365").
  6. Click Change...

  8. Look for the setting that says Mail to keep offline.
  9. You’ll see a slider.
  10. Move the slider to select a shorter time period, such as 6 months or 3 months.
  11. (This tells Outlook to only keep recent emails locally.)

  13. Click Next, then Done.
  14. Restart Outlook to apply the changes.
The offline file will slowly begin to shrink over time. It unfortunately doesn't happen instantly, and will take a little time. It'll start pruning old emails as you leave Outlook idle.
You can nudge it into action by forcing a full Send and Receive:

  1. Click the Send/Receive tab at the top.
  2. In the Send/Receive section, click:
  3. Send/Receive All Folders
  4. If you want to keep tabs on what it's doing, you can click Show Progress too

It may take about 10 minutes to nudge it and reduce the file size of my cache

We can also rebuild the cache.. this takes a while to sync but the cache file will be a lot smaller and cleaner, but there's a few more steps:

  1. Open Outlook.
  2. Click File âž” Account Settings âž” Account Settings.
  3. In the Email tab, click once on your email account (it should say “Microsoft Exchange” or “Office 365”).
  4. Then click Data Files (above the account list).
  5. You will see your mailbox listed with a location — click Open File Location.

  7. A folder will open showing a file ending in .ost. (or it may not show the extension)
  8. Close Outlook completely (very important — Outlook must not be running at this point).
  9. In the folder that stayed open, right-click the .ost file and choose Rename.
  10. Add .old to the end of the file name.
  11. (For example: outlook.ost.old)
  12. Reopen Outlook.
  13. Outlook will automatically create a new storage file and download only your recent emails according to the new cache setting.

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