Outlook Not Sending, Receiving, or Syncing, Real Fixes for 2026
Why Outlook Stops Sending, Receiving, or Syncing
Picture this: it's 9 AM, you have a time-sensitive email sitting in your Outbox, and Outlook is just... sitting there. No error. No movement. The status bar at the bottom says "Sending", but nothing ever actually sends. Or maybe you're getting hammered with a password prompt every time you open Outlook, or your inbox simply stopped updating an hour ago while Outlook claims it's perfectly connected. I've seen all three of these scenarios play out on hundreds of machines, and I know exactly how maddening they are.
The frustrating part is that Outlook's error messages are almost never helpful. "The connection to Microsoft Exchange is unavailable" tells you nothing about why the connection dropped. "Outlook not sending, receiving, or syncing" is a symptom. The causes are usually one of five things, and once you know which one you're dealing with, the fix is actually pretty straightforward.
Here's a breakdown of what's actually going wrong under the hood:
Authentication failures. Classic Outlook for Windows has a known behaviour where the Logon network security setting on your Exchange account gets set to something other than Anonymous Authentication. When this happens, Outlook enters an endless loop of asking for your credentials while displaying "trying to connect...", and if you cancel, you get the "Exchange is unavailable" message. This hits users on Outlook 2007, 2010, and some builds of 2013 especially hard.
Modern authentication conflicts. If your organisation recently enabled modern authentication for Exchange Online in Microsoft 365, Outlook can show "Disconnected" in the status bar if your primary Windows sign-in account doesn't match the account you're using for the mailbox. This is a known issue caused by a miscommunication between Office and Windows where Windows hands over the wrong credential entirely.
Corrupted or misconfigured data files. Your .pst or .ost file is Outlook's local database. When it gets corrupted, from an abrupt shutdown, a full disk, or a bad sync, you start seeing sync failures, missing emails, and the dreaded error 0x8004010F when Outlook tries to send or receive.
Send/Receive group misconfiguration. Outlook uses Send/Receive groups to schedule when it polls your mail server. If this gets misconfigured, say, your account was removed from the group, or the schedule got set to manual-only, email piles up in the Outbox and never moves until you hit F9.
Outlook and OWA synchronisation conflicts. If you're working across both Classic Outlook for Windows and Outlook Web Access (OWA), certain settings or folder states can end up out of sync between the two clients, causing one or both to show stale data or miss new messages entirely.
The good news: every one of these is fixable. Some take two minutes; others need you to get into the registry. This guide walks through all of them. Browse all Microsoft fix guides →
The Quick Fix, Try This First
Before you go digging into Control Panel or the registry, do this. It resolves Outlook not sending, receiving, or syncing for roughly 40% of the cases I encounter.
Step 1: Force a manual Send/Receive cycle. Press F9 in Outlook, or go to Send/Receive > Send/Receive All Folders. Watch the status bar at the bottom. If you see a progress indicator run through and emails start moving, great, your Send/Receive schedule is just broken or paused. Fix that by going to Send/Receive > Send/Receive Groups > Define Send/Receive Groups and making sure "Schedule an automatic send/receive every X minutes" is checked with a sensible interval (5–10 minutes is typical).
Step 2: Check your connection status. Hold Ctrl and right-click the Outlook icon in your system tray. You should see a "Connection Status..." option. Click it. Look at the Connection column for your account, it should say "Established." If it says "Disconnected" or "Trying," you have a deeper connectivity or authentication issue and need to keep reading this guide.
Step 3: Restart Outlook in safe mode. Close Outlook completely, then press Win + R and type outlook.exe /safe and hit Enter. Safe mode disables all add-ins. If Outlook suddenly syncs fine in safe mode, you have a misbehaving add-in. Go to File > Options > Add-ins > COM Add-ins > Go and start disabling add-ins one by one until you find the culprit.
Step 4: Check whether the issue is account-specific or global. If you have multiple accounts in Outlook, do they all fail, or just one? A single account failing usually points to authentication or data file issues. All accounts failing at once usually points to a network problem, a firewall rule, or a proxy blocking Outlook's connections to Microsoft 365 endpoints.
If none of those quick checks resolves Outlook not sending, receiving, or syncing on your machine, move into the step-by-step fixes below.
This step is often skipped, but it's the right starting point, especially if email is piling up in your Outbox without generating any error code at all. Outlook's Send/Receive groups control which accounts sync, at what interval, and in what direction. One misconfigured checkbox here and your Outlook keeps emails stuck in outbox indefinitely.
First, fully exit Outlook. Don't just close the window, right-click the Outlook icon in your system tray and choose Exit. Then reopen it.
Now go to Send/Receive in the ribbon and click Send/Receive Groups > Define Send/Receive Groups (or press Ctrl + Alt + S).
In the dialog that opens, click Edit for your active group (usually called "All Accounts"). On the left panel you'll see each email account. Make sure your account has a checkmark next to it and that both "Include the selected account in this group" and "Send mail items" and "Receive mail items" are all checked. If your account somehow got removed from the group, which can happen after an Outlook repair or profile update, it will sit completely silent.
Back on the main Send/Receive Groups screen, confirm that "Schedule an automatic send/receive every [X] minutes" is enabled under "When Outlook is Online." Set it to 5 or 10 minutes if it's been switched off.
Click Close, then press F9 to trigger a manual cycle. If your stuck emails start moving and new mail starts arriving, you've found your problem. If Outlook throws an error code during the sync attempt, particularly 0x8004010F, move on to Step 2.
Error 0x8004010F is one of the most common Outlook sync error codes. The full message usually reads something like: "The operation failed. An object cannot be found." What's actually happening is Outlook can't locate or read its local data file, your .pst (personal folders) or .ost (offline Outlook data) file. It could be corrupted, or the path pointing to it could be wrong.
Microsoft provides a built-in repair tool called ScanPST.exe (also called the Inbox Repair Tool). Here's how to use it:
First, find the path to your data file. In Outlook, go to File > Account Settings > Account Settings, then click the Data Files tab. Note the file path listed there, copy it.
Next, find ScanPST.exe on your machine. Its location depends on your Office installation:
# For Microsoft 365 / Office 2019 / Office 2016 (64-bit):
C:\Program Files\Microsoft Office\root\office16\SCANPST.EXE
# For Office 2016 (32-bit on 64-bit Windows):
C:\Program Files (x86)\Microsoft Office\root\office16\SCANPST.EXE
# For Office 2013:
C:\Program Files\Microsoft Office\Office15\SCANPST.EXEOpen ScanPST.exe, click Browse, navigate to your data file path, and click Start. It'll scan the file and report errors. If it finds any, click Repair. Make sure the "Make backup of scanned file before repairing" checkbox is ticked, you want that safety net.
After the repair completes, reopen Outlook and try sending/receiving. In many cases, this eliminates the 0x8004010F error and restores normal sync behaviour completely.
If Outlook is stuck on "trying to connect..." and keeps demanding your password, especially on Outlook 2007, 2010, or older builds of 2013, the Logon network security setting is almost certainly wrong. The setting controls how Outlook authenticates with the Exchange server, and when it's set to anything other than Anonymous Authentication, Outlook enters a credential loop it can't escape from.
I want to be honest with you: this setting has a confusing name. "Anonymous Authentication" in this context doesn't mean your email is anonymous, it just means Outlook hands off authentication to Exchange's own security layer rather than trying to negotiate it separately. Microsoft confirmed this is the correct setting for Exchange Online connections in Classic Outlook.
Here's how to change it:
- Fully exit Outlook.
- Open Control Panel. In Windows 10 or 11: press Win + S, type control panel, press Enter.
- Find and double-click Mail (you may need to switch to Large Icons view to find it).
- Click Show Profiles, select your Outlook profile name, and click Properties.
- Click E-mail Accounts.
- Select your Exchange or Microsoft 365 account and click Change.
- In the Change Account dialog, click More Settings.
- In the Microsoft Exchange dialog that opens, click the Security tab.
- In the Logon network security dropdown, select Anonymous Authentication.
- Click OK, then Next, then Finish, then Close on Account Settings, then Close on Mail Setup, then OK.
Reopen Outlook. If the password prompts stop and mail starts flowing, you're done. If Outlook still shows "Disconnected" after this, move to Step 4, which covers the modern authentication issue.
This one is tricky because it looks like an authentication failure, but it's actually an account mismatch problem. Here's the scenario: your organisation turned on modern authentication for Exchange Online in Microsoft 365, and now Outlook shows "Disconnected" in the status bar even though your internet connection is fine and your password is correct.
What's happening: when modern authentication is active, Office talks to Windows to get the right credential. But if the account you use to sign in to Windows (your primary Windows account) is a Microsoft 365 account that's different from the mailbox you're trying to access in Outlook, Windows hands over the wrong credential. Outlook can't connect because it's presenting the wrong account to Exchange entirely.
This gets worse when you have multiple mailboxes in a single Outlook profile where at least one of them uses a sign-in account that doesn't match the Windows account.
The most reliable fix here is to run Microsoft's self-diagnostic tool. In your browser, navigate to the Microsoft 365 admin support portal and search for the "Diag: Outlook keeps asking for my password" diagnostic. It runs automated checks against your tenant configuration and mailbox settings and walks you through specific remediation steps based on what it finds.
If you're in an enterprise environment and can't access that tool, the workaround is to remove the conflicting account from the Outlook profile and re-add it, this time signing in with the correct account that matches the mailbox. Go to File > Account Settings > Account Settings, select the affected account, click Remove, then click New to re-add it and authenticate fresh with the correct credentials.
After reconnecting, watch the status bar. It should shift from "Disconnected" to "Connected to Microsoft Exchange" within 30–60 seconds if the credential mismatch is resolved.
If you've worked through the previous steps and Outlook is still not sending, receiving, or syncing correctly, it's time to bring in Microsoft's automated repair tool: the Microsoft Support and Recovery Assistant, often called Sara. This is a free tool from Microsoft that runs a battery of diagnostic checks specific to your machine, your Outlook version, and your Microsoft 365 account configuration.
Sara goes beyond what manual troubleshooting can do in a reasonable time. It checks things like your Office activation state, Autodiscover configuration, proxy settings, certificate trust chains, OAuth token caches, and connectivity to Microsoft 365 service endpoints, all automatically.
To get it: search for "Microsoft Support and Recovery Assistant" in your browser and download it from the official Microsoft download page (look for the microsoft.com domain). Install it, open it, and select Outlook from the product list. Then select the specific problem you're experiencing, "Outlook keeps asking for my password," "Outlook won't send or receive," or "Outlook can't connect to Exchange."
Walk through the prompts. Sara will ask you to sign in with your Microsoft 365 account so it can test connectivity end-to-end. Let it run, the scan takes 3–5 minutes. At the end, it gives you a results screen showing exactly what it found and what it fixed or recommends.
In my experience, Sara catches Autodiscover misconfigurations and OAuth token corruption issues that are genuinely hard to track down manually. If Sara comes back with no issues found but Outlook is still broken, that's actually useful information, it points toward a server-side problem or a network-level block, which is where the advanced section of this guide comes in.
Advanced Troubleshooting for Outlook Sync Failures
You've worked through the standard fixes and Outlook is still not sending, receiving, or syncing. Here's where we go deeper. These approaches cover domain-joined machines, Group Policy conflicts, registry-level authentication settings, and Event Viewer analysis.
Check the Registry for Authentication Mode
Microsoft's documentation confirms that the Logon network security setting, specifically whether Anonymous Authentication is active, is stored in the registry inside your Outlook profile. If you want to verify what's actually configured (or if you're deploying a fix across multiple machines), here's where to look:
# For Outlook 2013:
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Profiles
# For Outlook 2010 and 2007:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\ProfilesUnder your profile key, navigate into 9375CFF0413111d3B88A00104B2A6676, then through the numbered subkeys (00000001, 00000002, etc.) until you find the one with an Account Name binary value matching your SMTP address. From there, follow the Service UID GUID to locate your account's specific configuration subfolder, then look for the 00036619 binary value. If its data reads 01 f0 00 80, Anonymous Authentication is active. Any other value means it's not, and that's your problem.
Critical warning: Microsoft explicitly states that modifying Outlook profiles via the registry is not supported and can leave your profile in an unsupported state. Back up the registry before touching anything here. If you're not comfortable with registry editing, use the Control Panel > Mail path from Step 3 instead.
Group Policy Overrides
In enterprise environments, Group Policy can override your local Outlook security settings, meaning you change the setting in Control Panel, it looks correct, but on next login GPO silently resets it. Check with your IT administrator whether an Outlook authentication policy is being applied via ADMX templates. The relevant policy path is usually under User Configuration > Administrative Templates > Microsoft Outlook [version] > Account Settings > Exchange.
Event Viewer Analysis
When Outlook fails silently, no error code, no prompt, just "Disconnected", Event Viewer often has the real answer. Open Event Viewer (Win + R, type eventvwr.msc), then navigate to Windows Logs > Application. Filter by Source = "Outlook" or look for error events from "MSExchange" or "Microsoft Office." Common event IDs to look for include 27 (connection failure), 64 (certificate validation failure), and 1000 (application crash during send/receive). The error descriptions in these events are far more specific than anything Outlook shows in its UI.
Synchronisation Conflicts Between Outlook and OWA
If you actively use both Classic Outlook for Windows and Outlook Web Access and you're seeing inconsistent data, emails that show as read in OWA but unread in Outlook, or folders that are present in one but not the other, the sync conflict is usually caused by cached mode behaviour. Try switching Outlook out of Cached Exchange Mode temporarily: go to File > Account Settings > Change > More Settings > Advanced and uncheck "Use Cached Exchange Mode." This forces Outlook to talk directly to the Exchange server for every operation, which confirms whether the issue is in the local cache or on the server side.
Prevention & Best Practices
Once you've fixed Outlook not sending, receiving, or syncing, you don't want to be back here in three months doing this again. Here's how to keep Outlook running reliably.
Keep Outlook updated. Microsoft quietly pushes authentication fixes, Autodiscover improvements, and sync reliability patches through regular Office updates. Outlook 2016 and certain builds of Outlook 2013, for example, were updated to remove the problematic Logon network security setting entirely, making the whole Anonymous Authentication dance unnecessary. Go to File > Office Account > Update Options > Update Now and make this a monthly habit.
Monitor your .pst and .ost file sizes. When these files balloon past 10–15 GB, Outlook performance degrades and corruption risk increases sharply. Microsoft's own documentation flags "performance issues with too many items or folders" as a known failure mode. Archive older emails regularly using File > Tools > Clean Up Old Items, and consider moving large attachments out of your mailbox and into SharePoint or OneDrive.
Don't ignore the "Only some emails are synchronized" warning. If you ever notice that your Outlook inbox doesn't match what you see in OWA, don't just shrug it off. That gap usually means your Cached Exchange Mode sync window is too short, or there's a data file issue developing. Check your sync window under Account Settings > Change > More Settings > Advanced > Mail to keep offline and make sure it covers the period you need.
Create a clean Outlook profile now, before you need it. Go to Control Panel > Mail > Show Profiles and create a second profile configured with your email account. Don't use it as your default, just have it ready. When your primary profile becomes corrupted or broken, switching to the backup profile takes 30 seconds and avoids hours of troubleshooting.
- Enable automatic Office updates so Outlook gets authentication and sync patches as soon as they ship.
- Set a calendar reminder every 3 months to check your .ost file size and archive anything over 10 GB.
- Add the Microsoft Support and Recovery Assistant shortcut to your desktop, it's free, fast, and saves an hour of manual diagnosis when something breaks.
- If you're on a domain-joined machine, ask your IT team whether a modern authentication policy is applied via Group Policy, knowing this in advance saves a lot of confusion when settings don't stick.
Frequently Asked Questions
Why is my email stuck in Outbox and won't send even though I have internet?
This almost always comes down to one of two things: either your Send/Receive schedule got set to manual (so Outlook never automatically pushes the email out), or there's an authentication failure blocking the connection to your mail server. Start by pressing F9 to force a manual send, if the email goes through, fix your Send/Receive schedule via Send/Receive > Send/Receive Groups > Define Send/Receive Groups. If F9 produces an error code, particularly 0x8004010F, your Outlook data file likely needs repair using ScanPST.exe.
Why does Outlook keep asking for my password over and over?
On Classic Outlook for Windows with older versions (2007, 2010, and some 2013 builds), the most common cause is the Logon network security setting being wrong. Go to Control Panel > Mail > Show Profiles > Properties > E-mail Accounts > Change > More Settings > Security tab, and set the Logon network security dropdown to Anonymous Authentication. On newer Outlook versions where that setting has been removed, the cause is usually a modern authentication account mismatch, run Microsoft's self-diagnostic tool ("Diag: Outlook keeps asking for my password") to identify the specific cause for your tenant configuration.
What exactly is error 0x8004010F in Outlook and how do I fix it?
Error 0x8004010F means Outlook failed to find or read an object it was looking for, almost always your local data file (.pst or .ost). The file path may be wrong, or the file itself may be corrupted. Fix it by running ScanPST.exe, which is Microsoft's built-in Inbox Repair Tool. Find it at C:\Program Files\Microsoft Office\root\office16\SCANPST.EXE for Office 2016 and later, point it at your data file (found under File > Account Settings > Data Files tab), run the scan, and let it repair any errors it finds.
Why does Outlook show "Disconnected" after my company enabled modern authentication?
This is a known issue where Office and Windows get into a miscommunication about which credential to use. It happens most often when your primary Windows sign-in account is a Microsoft 365 account that doesn't match the mailbox account in your Outlook profile, Windows ends up handing the wrong credential to Exchange. The quickest workaround is to remove the affected mailbox from your Outlook profile and re-add it, signing in with the correct account. If the problem affects multiple users in your organisation, it's worth running the "Diag: Outlook keeps asking for my password" diagnostic in the Microsoft 365 admin portal.
My Outlook inbox shows different emails than what I see in OWA, how do I fix the sync?
When Classic Outlook for Windows and OWA show different data, the culprit is usually Cached Exchange Mode. Outlook stores a local copy of your mailbox and syncs periodically, if that sync breaks down or the cached window is too short, the two views diverge. First check your sync window under Account Settings > Change > More Settings > Advanced (set "Mail to keep offline" to All). Then try temporarily disabling Cached Exchange Mode entirely to see if the mismatch disappears. If it does, your .ost cache file is the problem, delete it (Outlook will rebuild it automatically from the server) and re-enable Cached Exchange Mode.
Is it safe to use ScanPST.exe on a large .pst file without losing emails?
Yes, ScanPST.exe is designed specifically to repair Outlook data files without data loss, and it makes a backup of the original file before making any changes (as long as you leave the "Make backup of scanned file before repairing" checkbox ticked, which it is by default). That said, if your .pst file is severely corrupted, ScanPST may not be able to recover everything. In worst-case scenarios it creates a "Recovered" folder with whatever it could salvage. For large files over 10 GB, the scan can take 20–40 minutes, let it run to completion without interrupting it.