Summary

If Outlook is not showing new emails, your Sent Items are not appearing on other devices, or folders seem stuck with old messages, Outlook has likely lost its connection to the mail server or its local cache has become corrupted. This article walks you through every user-level fix, from quick checks to full profile rebuilds.

In this guide

• 1. Check the Connection Status Bar
• 2. Disable Work Offline Mode
• 3. Force a Manual Send/Receive
• 4. Adjust Cached Exchange Mode Sync Window
• 5. Clear the Outlook Cache (OST File Rebuild)
• 6. Fix Sync Issues in New Outlook for Windows
• 7. Re-Create the Outlook Mail Profile
• 8. Verify in Outlook on the Web

Before You Start

• An active internet connection — verify by opening a webpage in your browser.
• If your organization uses a VPN, connect to it before troubleshooting.
• Save any emails you are drafting before starting — some methods require restarting Outlook.

Instructions

1. Check the Connection Status Bar

Outlook displays its connection state at the bottom of the window. This is the fastest way to determine the type of sync problem.

1. Look at the bottom-right corner of the Outlook window.
2. The status bar shows one of the following:
   • Connected to: Microsoft Exchange — Outlook is connected. The sync issue is likely cache-related (skip to Method 4).
   • Disconnected — Outlook cannot reach the mail server. Continue to Method 2.
   • Trying to connect… — Outlook is actively attempting to reconnect. Wait 30 seconds. If it does not resolve, continue to Method 2.
   • Need Password — Outlook's authentication has expired. Click the prompt, re-enter your password, and check Remember my credentials.
   • Working Offline — You are in offline mode. Go directly to Method 2.
3. If you do not see a status bar, right-click the bottom bar of the Outlook window and ensure Connection Status is checked.

Verification: Once the status bar reads "Connected to: Microsoft Exchange," Outlook should begin syncing automatically within 30 seconds.

2. Disable Work Offline Mode

Work Offline mode stops Outlook from communicating with the mail server entirely. It is a single menu click, so it gets switched on by accident.

1. Click the Send / Receive tab in the Outlook ribbon.
2. Look at the Work Offline button on the right side of the ribbon.
3. If the button appears shaded or highlighted, Work Offline is active. Click it once to turn it off.
4. Watch the status bar at the bottom — it will change from Working Offline to Connected to: Microsoft Exchange within a few seconds.
5. Click Send / Receive All Folders (or press F9) to force an immediate sync.

Verification: The status bar shows "Connected" and new emails begin arriving within 30 seconds.

3. Force a Manual Send/Receive

If Outlook is connected but not pulling new mail on its own, the automatic sync interval may have been disrupted.

1. Click the Send / Receive tab.
2. Click Send / Receive All Folders (or press F9).
3. Watch the progress bar at the bottom of the screen. If it completes without errors, emails should appear.
4. If only one folder is stuck, right-click that specific folder in the folder pane and select Update Folder.
5. To verify the automatic sync interval is set correctly:
   • Click Send / Receive tab > Send/Receive Groups > Define Send/Receive Groups.
   • Ensure Schedule an automatic send/receive every is checked and set to 5 minutes or less.
   • Click Close.

Verification: After pressing F9, the progress bar completes and new emails appear in the Inbox.

4. Adjust Cached Exchange Mode Sync Window

Cached Exchange Mode stores a local copy of your mailbox for faster access. By default, it may only sync the last 1-3 months of mail — meaning older emails appear missing.

1. Click File > Account Settings > Account Settings.
2. On the Email tab, select your email account and click Change.
3. Look for the Mail to keep offline slider (or Download email for the past dropdown).
4. Move the slider to the right to increase the time window. Options include 1 month, 3 months, 6 months, 1 year, 2 years, or All.
5. Click Next > Done.
6. Outlook will begin downloading the additional mail in the background. Large mailboxes may take 15-30 minutes to finish syncing.

Verification: After the download completes, older emails that were previously missing appear in the folder. The status bar shows "All folders are up to date."

5. Clear the Outlook Cache (OST File Rebuild)

If the local cache file (the .ost file) becomes corrupted, Outlook may show outdated data, skip emails, or fail to sync specific folders. Rebuilding it forces Outlook to download a fresh copy from the server.

1. Close Outlook completely.
2. Press Windows + R to open the Run dialog.
3. Type outlook.exe /resetfolders and press Enter. This resets the default folder structure without deleting data.
4. If the issue persists after restarting, close Outlook again and rebuild the OST file:
   • Press Windows + R, type %localappdata%\Microsoft\Outlook and press Enter.
   • Locate the .ost file (it is named after your email address, e.g., [email protected]).
   • Rename the file by adding .old to the end (e.g., [email protected]). Do not delete it — renaming preserves a backup.
5. Open Outlook. It will detect the missing OST file and create a new one, downloading all mail from the server.
6. Wait for the initial sync to complete. Progress is shown in the status bar and Send/Receive progress dialog.

Verification: Outlook opens with a fresh cache and begins downloading email. All folders should populate within 15-60 minutes depending on mailbox size. The renamed .old file can be deleted once you confirm everything synced correctly.

6. Fix Sync Issues in New Outlook for Windows

The New Outlook app (the simplified version replacing the classic desktop app) uses a different sync engine. If sync stops working in New Outlook, the troubleshooting steps differ slightly. If you are not certain which version you are running, Understanding Outlook Versions — Classic vs. New vs. Web shows you how to tell.

1. Open New Outlook.
2. Click the Settings gear icon in the top-right corner.
3. Click Accounts > select your email account.
4. Click Manage and verify the account status shows Connected.
5. If the account shows an error, click Fix account and follow the prompts to re-authenticate.
6. If emails are still not syncing, reset the app:
   • Go to Settings > Apps > Installed apps.
   • Find Outlook (new), click the three dots (…), and select Reset.
   • Reopen New Outlook and sign in again.

Verification: After re-authenticating or resetting, New Outlook should sync all folders within a few minutes. Check both Inbox and Sent Items.

7. Re-Create the Outlook Mail Profile

If the sync issue persists after rebuilding the OST file, the mail profile itself may be corrupted. Creating a new profile provides a completely clean start.

1. Close Outlook completely.
2. Press the Start key, type Control Panel, and press Enter.
3. Click Mail (Microsoft Outlook).
4. Click Show Profiles.
5. Click Add and name the new profile (e.g., NewProfile).
6. Follow the prompts to enter your email address and sign in. Outlook will auto-discover your server settings.
7. Once the profile is created, select Always use this profile and choose NewProfile from the dropdown.
8. Click OK and open Outlook. It will open with the new profile and begin downloading your mailbox.

Verification: Outlook opens with the new profile and syncs all folders from scratch. The old profile can be deleted once you confirm everything is working.

8. Verify in Outlook on the Web

Before spending more time troubleshooting the desktop app, confirm whether the issue is local to your PC or server-side.

1. Open a browser and go to https://outlook.office.com.
2. Sign in with your work email and password.
3. Check your Inbox and Sent Items for the missing emails.
4. If the emails appear in Outlook on the Web but not in the desktop app, the issue is with the local cache — Methods 5 or 7 will resolve it.
5. If the emails are also missing in Outlook on the Web, the issue is server-side. Ask your IT helpdesk to check your mailbox for a server-side rule, a retention policy, or a full-quota block — name the folder the emails are missing from and the date range you expected them in. Before you raise that ticket, rule out the junk folder, the Focused Inbox Other tab, a rule of your own, and a full mailbox — How to Fix Outlook Not Receiving Emails covers each check.

Verification: This method does not fix the problem directly, but it narrows down whether the root cause is local (desktop app) or server-side (requires IT intervention).

Troubleshooting

DANGER

If Outlook repeatedly asks for your password after syncing fails, do not keep re-entering it. This can trigger an account lockout. Instead, sign out of Outlook completely, clear your Windows credentials (search for Credential Manager in the Start menu, find entries for MicrosoftOffice and remove them), then restart Outlook and sign in once.

Symptom / Error	Potential Cause	Solution
Status bar says "Disconnected"	Network or VPN issue	Check your internet connection and reconnect to VPN if required.
Status bar says "Working Offline"	Work Offline mode enabled	Click Send / Receive > Work Offline to disable (see Method 2).
Status bar says "Need Password"	Authentication expired	Click the prompt, re-enter credentials. Clear Credential Manager if it loops.
Emails appear in webmail but not desktop	Corrupted local cache (OST)	Rename the OST file and let Outlook rebuild (see Method 5).
Only one folder is not syncing	Folder-level sync stall	Right-click the folder > Update Folder, or run outlook.exe /resetfolders.
Old emails disappeared	Cached Mode sync window too short	Increase the "Mail to keep offline" slider (see Method 4).
Sync works but is extremely slow	Large mailbox (50 GB+)	Reduce the Cached Mode window to 6 months instead of All. Large caches slow sync.
"Outlook data file cannot be accessed"	Corrupted or locked OST file	Close all Office apps, rename the OST file, and restart Outlook (see Method 5).
Sent emails not appearing in Sent Items	"Save to Sent Items" disabled	Go to File > Options > Mail > ensure Save copies of messages in the Sent Items folder is checked.

Related Articles

• How to Fix Outlook Not Responding or Freezing
• How to Fix Outlook Not Receiving Emails
• How to Fix "Working Offline" in Outlook
• How to Fix Outlook Running Slowly
• How to Fix Outlook Keeps Asking for Password
• How to Manage Your Outlook Mailbox Storage

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