Your emails have stopped updating. You sent something hours ago, but it still sits in your outbox. Maybe you got a message on your phone, but it refuses to show up on your laptop. This syncing headache is more common than you think, and it can really mess up your day when you’re trying to stay on top of work or personal stuff.
Here’s what you need to know about fixing this issue. We’ll cover why it happens, what’s probably causing your specific problem, and the exact steps you can take to get your Outlook 365 back in sync across all your devices.
What’s Going On With Your Email
Syncing means all your devices talk to each other and share the same information. Your laptop, phone, and tablet should all show the same emails, folders, and calendar events at the same time. When something breaks that connection, you end up with different information on different devices. It’s like having multiple copies of the same notebook that don’t match anymore.
Several things happen when Outlook stops syncing properly. You might send an email that gets stuck and never actually leaves. Or you’ll read and delete messages on your phone, but they keep showing up as new on your computer. Appointments you added on one device won’t appear on another, which can lead to missed meetings.
This problem gets worse the longer you let it sit. Your sent items might pile up in the outbox. Important messages could be sitting on the server, but you’ll never see them. Contacts you added or changed on your phone won’t update on your desktop. Tasks and reminders can get completely out of sync too.
The thing is, your email client needs a smooth connection to Microsoft’s servers to keep everything updated. Any hiccup in that connection, or a setting that got changed accidentally, can throw the whole system off. Sometimes it’s a simple fix. Other times, you might need to check a few different things before you find the culprit.
365 Outlook Not Syncing: Common Causes
Several factors can disrupt the syncing process in Outlook 365. Let’s look at what’s usually behind this frustrating issue so you can figure out which one matches your situation.
1. Poor or Unstable Internet Connection
Your internet connection is the highway your email travels on. If that highway has potholes or keeps closing down, your messages can’t get through. This happens more often than you’d think, especially if you’re on spotty WiFi or if your internet provider is having a bad day.
Even a connection that seems fine can cause problems. You might be able to browse websites just fine, but Outlook needs a steady, reliable connection to sync properly. Brief dropouts that you wouldn’t notice during regular browsing can interrupt the syncing process.
Mobile users face this a lot when switching between WiFi and cellular data. That moment of transition can break the sync, leaving some items stuck in limbo until you manually refresh or restart the app.
2. Outdated Outlook Version
Running an old version of Outlook is like trying to speak an outdated language. Microsoft constantly updates their servers and security protocols. Your older app version might not understand the new commands or security requirements, so it can’t sync properly anymore.
These updates happen quietly in the background for most apps. But if you’ve disabled automatic updates or if something went wrong during a previous update, you could be running outdated software without realizing it.
3. Sync Settings Got Changed
Sometimes the settings that control how often and how much Outlook syncs get adjusted by accident. Maybe you were trying to save battery life on your phone and changed some settings. Or a recent update reset things to default values that don’t work well for your setup.
Outlook has different sync intervals for different types of data. Your emails might sync every few minutes, but your calendar could be set to sync less frequently. If these settings got bumped to longer intervals or turned off completely, you’ll notice delays or complete failures.
Mailbox size limits can affect syncing too. If you’ve set Outlook to only sync recent emails to save space, older messages won’t appear. You might think syncing is broken when really it’s working exactly as configured, just not the way you need it to.
4. Corrupted Cache or Data Files
Think of the cache like a filing cabinet where Outlook keeps copies of your emails and settings for quick access. Over time, this filing cabinet can get messy. Files can become damaged, or old information can conflict with new updates.
This corruption happens gradually. Maybe your computer shut down unexpectedly while Outlook was working. Or perhaps you’ve been using the app for months without clearing out temporary files. Small errors add up until the whole system starts acting weird.
Your Outlook profile, which stores all your account settings and local data, can also get corrupted. When this happens, the app can’t figure out what to sync or how to sync it. Everything looks fine on the surface, but underneath, the instructions are garbled.
5. Too Many Emails or Large Attachments
Trying to sync thousands of emails at once, especially if they have big attachments, is like trying to pour a gallon of water through a straw. It can work, but it takes forever and often gets stuck partway through.
This happens most often right after you set up a new device or reinstall Outlook. The app tries to download your entire mailbox at once, and the sheer volume overwhelms the process. Older devices with less memory struggle even more with this.
6. Server or Account Issues
Sometimes the problem isn’t on your end at all. Microsoft’s servers could be having technical difficulties. Your company’s email server might be down for maintenance. Or there could be an issue with your specific account that prevents proper syncing.
Account verification problems fall into this category too. If Microsoft suspects unusual activity or if your password recently changed but didn’t update everywhere, the servers might block sync requests as a security measure.
365 Outlook Not Syncing: How to Fix
Getting your Outlook syncing again usually involves working through some straightforward fixes. Let’s go through the most effective solutions that handle the majority of syncing problems.
1. Check Your Internet Connection
Start with the basics because they matter more than you’d think. Open a web browser and try loading a few different websites to verify your connection actually works. If pages load slowly or don’t load at all, that’s your problem right there.
Try switching networks if possible. If you’re on WiFi, switch to your phone’s hotspot or vice versa. This tells you whether the issue is with your specific network or with Outlook itself. Sometimes just disconnecting and reconnecting to WiFi can shake loose whatever was causing the problem.
For mobile users, check if you’ve accidentally enabled airplane mode or if mobile data is turned off for the Outlook app specifically. Go into your phone’s settings and make sure Outlook has permission to use cellular data.
2. Restart Outlook and Your Device
Close Outlook completely. Don’t just minimize it or leave it running in the background. Actually shut it down. On Windows, right-click the Outlook icon in your taskbar and choose Close. On Mac, quit the application fully. On mobile, swipe it away from your recent apps.
Wait about 30 seconds. This gives the system time to clear out any temporary glitches in memory. Then reopen Outlook and see if it starts syncing. This simple restart fixes things more often than you’d expect because it forces the app to reconnect fresh to the servers.
If that doesn’t work, restart your entire device. Power it all the way off, wait a few seconds, then turn it back on. This clears out deeper system issues that might be interfering with Outlook’s ability to sync.
3. Force a Manual Sync
Sometimes Outlook needs a little push to get going again. Open Outlook and look for the Send/Receive button. On desktop versions, it’s usually right there in the ribbon at the top. Click it to force Outlook to check for new messages and send anything waiting in your outbox.
You can also right-click on your account name in the folder list and choose “Update Folder.” This tells Outlook to refresh everything for that specific account. If you have multiple accounts set up, you might need to do this for each one.
Mobile apps have a pull-to-refresh feature. Just swipe down on your inbox like you’re pulling down a window shade. The app will check for new messages and try to sync whatever’s pending. Do this a few times if the first attempt doesn’t work.
4. Update Outlook to the Latest Version
Keeping your software current fixes a surprising number of problems. On Windows, open Outlook and go to File, then Office Account, then Update Options. Click “Update Now” and let it install any available updates. This can take a few minutes, so be patient.
Mac users should open the App Store and click on Updates in the sidebar. Look for any Microsoft Office or Outlook updates and install them. The App Store handles the whole process automatically once you click the update button.
For mobile devices, open your app store (Google Play or Apple App Store) and search for Outlook. If an update is available, you’ll see an “Update” button instead of “Open.” Tap it and wait for the new version to download and install. Your app will restart automatically when it’s done.
Make sure you’re connected to WiFi for these updates. They can be large files, and you don’t want to eat up your mobile data or have the download interrupted by a weak cellular signal.
5. Clear the Outlook Cache
Getting rid of old cached data often solves stubborn syncing issues. On Windows, close Outlook first. Then open File Explorer and paste this into the address bar: %localappdata%\Microsoft\Outlook. You’ll see several files with the .ost extension. These are your offline data files.
Back up these files by copying them to another folder, just in case. Then delete the originals. When you restart Outlook, it will create fresh cache files and download everything new from the server. This process can take a while if you have a lot of emails.
Mobile apps make this easier. Go to your phone’s settings, find the Outlook app, and look for an option to clear cache or clear data. On Android, it’s usually under Storage. On iPhone, you might need to delete and reinstall the app to fully clear the cache.
6. Check Your Sync Settings
Open Outlook settings and look for the sync options. On desktop, go to File, then Account Settings, then Account Settings again. Select your email account and click Change. You’ll see options for how much mail to keep offline and how often to sync.
Make sure “Download email from” is set to “All” or at least the past 12 months. If it’s set to a shorter period, older emails won’t sync. Check that automatic send/receive is enabled and set to run every few minutes.
On mobile, open the Outlook app settings (usually accessible from your profile icon). Look for sync settings or sync schedule. Make sure it’s set to sync automatically and that the sync window includes all the mail you need. Some phones also have battery-saving modes that restrict background syncing, so check your device’s battery settings too.
7. Remove and Re-add Your Account
If nothing else works, starting fresh with your account often does the trick. Open Outlook and go to Account Settings. Select your problem account and click Remove. This won’t delete your emails from the server, just from this device.
After removing the account, close Outlook completely. Restart it, then add your account back using the same email address and password. Outlook will set up everything from scratch, which can clear out whatever was causing the sync failure.
This solution takes the most time because Outlook needs to download all your emails again. But it fixes account-level corruption and settings issues that other methods can’t touch. Make sure you’re on a good internet connection before you start this process.
8. Contact Microsoft Support
If you’ve tried everything and Outlook still won’t sync, there might be a server problem or an issue with your specific account that only Microsoft can fix. Visit the Microsoft 365 support page or call their support line. Have your account information ready and be prepared to describe what you’ve already tried.
Your company’s IT department can help too if you use Outlook through work. They have access to server logs and can check if there’s a broader issue affecting multiple users. Sometimes they need to reset something on their end to get your account syncing again.
Wrapping Up
Syncing problems in Outlook 365 can stem from simple connection hiccups or deeper software issues. Most of the time, a restart or clearing your cache gets things moving again. Check your internet first, update your app, and make sure your settings allow proper syncing.
If basic fixes don’t work, removing and re-adding your account usually clears up stubborn problems. Keep your Outlook updated regularly to avoid compatibility issues. Your email is too important to stay broken, so work through these solutions until you find what fixes your specific situation.