Outlook Not Syncing Emails — How to Fix It

Outlook not syncing is one of the most disruptive email problems — messages are delayed, sent items do not appear, or the inbox simply stops updating. Most causes are straightforward to fix. Work through these steps in order and Outlook will usually be back to normal within a few minutes.

1. Check Your Internet Connection and Outlook Status

Before troubleshooting Outlook, confirm:

• Your internet connection is working — open a browser and load a page
• Outlook shows Connected in the status bar at the bottom of the window, not “Disconnected” or “Trying to connect”
• The Microsoft 365 service is not down — check status.office365.com for live outage information

If Outlook shows “Disconnected” in the status bar, the issue is the connection between Outlook and the mail server, not just slow sync.

2. Click Send/Receive

The quickest first step. Press F9 or go to the Send/Receive tab and click Send/Receive All Folders. This forces Outlook to sync immediately rather than waiting for the next automatic interval.

If you get an error message during Send/Receive, note the error number — it points to the specific cause.

3. Check Outlook is Not Working Offline

Outlook has a Work Offline mode that deliberately stops all sync. It is easy to enable accidentally.

1. Click the Send/Receive tab in the ribbon
2. Look at the Work Offline button — if it is highlighted/pressed, click it to go back online

When Work Offline is active, Outlook shows “Working Offline” in the bottom status bar.

4. Repair the Outlook Account

1. Go to File → Account Settings → Account Settings
2. Select your email account and click Repair
3. Follow the prompts — Outlook re-authenticates and tests the connection

This resolves most sync problems caused by credential expiry or server configuration changes. If your organisation recently changed the mail server settings or you updated your password, this step fixes it.

5. Update Your Password

If you recently changed your Microsoft 365 or email password, Outlook may be using the old one. Signs of this: Outlook keeps prompting for a password, or shows “Need password” in the status bar.

1. Go to File → Account Settings → Account Settings
2. Double-click your account
3. Update the password and click Next → Finish

Also check Windows Credential Manager: search for Credential Manager in Start → Windows Credentials. Look for any entries related to your email server or Microsoft 365 (MicrosoftOffice, MicrosoftOutlook, or your mail server address). Remove outdated entries and let Outlook prompt for fresh credentials.

6. Clear the Outlook Cache

Outlook maintains a local cache of your mailbox (an OST file). If this file becomes corrupted, sync breaks.

1. Close Outlook
2. Press Win + R, type %localappdata%\Microsoft\Outlook and press Enter
3. Find files with the .ost extension — these are your local cache files
4. Rename the OST file (e.g. add .old to the filename) rather than deleting it
5. Reopen Outlook — it creates a fresh OST file and re-syncs from the server

Re-syncing a large mailbox can take 20–30 minutes. Outlook is usable during this time but may show messages as loading.

7. Check Your Mailbox Sync Settings

Outlook can be configured to only sync recent email, leaving older messages on the server:

1. Go to File → Account Settings → Account Settings
2. Double-click your account → More Settings → Advanced
3. Check the Mail to keep offline slider — if set to 1 month, emails older than that are not synced locally
4. Increase this or set it to All to sync your full mailbox

8. Disable Add-ins

Faulty Outlook add-ins can interfere with sync. Start Outlook in safe mode (which disables all add-ins) to test:

1. Press Win + R, type outlook /safe and press Enter
2. If Outlook syncs correctly in safe mode, an add-in is the cause
3. Go to File → Options → Add-ins → Manage COM Add-ins → Go
4. Untick add-ins one at a time, restarting after each, until normal mode works

9. Repair Microsoft 365

If none of the above works, run the Office repair tool to fix corrupted Outlook files:

1. Go to Settings → Apps → Installed apps
2. Find Microsoft 365 or Microsoft Office
3. Click the three dots → Modify
4. Choose Quick Repair first (no internet needed). If that does not fix it, run Online Repair.

Related Guides

• How to Create a Rule in Outlook
• How to Search Emails in Outlook Effectively
• How to Set an Out of Office Reply in Outlook