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How to Clear Your Outlook Cache

If Outlook is showing outdated emails, missing messages, slow performance, or sync errors, clearing the cache often resolves the issue. This article walks you through how to do this safely on both the New and Classic Outlook for Windows desktop apps.

Before You Begin

  • Close Outlook completely before deleting any cache files. Files in use are locked and cannot be removed.
  • Cache clearing is safe for Exchange Online / Microsoft 365 accounts because your mail lives on the server and will re-download automatically.
  • If you use a POP3 account, do not delete your .ost or .pst files — your mail is stored locally and could be lost. Back up first.
  • After resetting, you may need to sign in again and re-download your mailbox. Initial sync can take some time on large accounts.

New Outlook for Windows

New Outlook is cloud-first, so most of your data is stored on the server. To refresh the local copy, use the built-in repair and reset options.

Option 1: Repair the App (Recommended First Step)

  1. Close Outlook
  2. Open Settings → Apps → Installed apps
  3. Find Outlook, click the ⋯ menu, and select Advanced options
  4. Scroll to the Reset section and click Repair
  5. Reopen Outlook

Repair preserves your data and fixes most common issues.

Option 2: Reset the App (Full Cache Clear)

If Repair doesn't resolve the issue:

  1. Follow steps 1–3 above.
  2. Under the Reset section, click Reset.
  3. Reopen Outlook and sign back in. Your mailbox will re-sync from the server.

Classic Outlook for Windows

Classic Outlook uses two main cache locations: the RoamCache folder (autocomplete, nicknames, recent contacts) and the OST file (your full offline mailbox copy).

Option 1: Clear the RoamCache

Use this if autocomplete suggestions are wrong or contacts aren't updating.

  1. Close Outlook
  2. Press Windows key + R to open the Run dialog

  3. Paste the following path and press Enter:

    %localappdata%\\Microsoft\\Outlook\\RoamCache

  4. Select all files in the folder and delete them
  5. Reopen Outlook; the cache will rebuild automatically

Option 2: Clear the OST File (Full Mailbox Cache)

Use this when the mailbox is out of sync, corrupted, or showing stale content.

  1. Close Outlook.

  2. Press Windows key + R, paste the path below, and press Enter:

    %localappdata%\\Microsoft\\Outlook

  3. Find the .ost file that matches your email address (for example, yourname@yourcompany.com.ost)
  4. Rename it by adding .old to the end, or delete it
  5. Reopen Outlook; a new OST file will be created, and your mail will re-download from the server

⚠️ Re-downloading a large mailbox can take anywhere from a few minutes to several hours, depending on mailbox size and connection speed.

Still Having Issues?

If clearing the cache doesn't resolve the problem, please reach out to support@contactmonkey.com with the following details so we can help faster:

  • Your Outlook version (New or Classic) and build number
  • The exact error message or behaviour you're seeing
  • A screenshot, if possible
  • The approximate time the issue started
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