Outlook is the backbone of business communication for millions of Canadian companies — and when it stops working, productivity comes to a halt. Whether Outlook will not open, keeps saying "Disconnected," refuses to send emails, freezes on the loading screen, or crashes the moment you click it, this guide covers 10 real, step-by-step fixes that resolve the most common Outlook issues across Office 2016, 2019, 2021, and Microsoft 365.
Fix 1 — Run Outlook in Safe Mode
Safe Mode disables all add-ins and starts Outlook with minimal configuration. If Outlook works in Safe Mode but crashes normally, a third-party add-in is almost certainly the cause.
How to open Outlook Safe Mode
Hold the Ctrl key and click the Outlook icon in your taskbar or Start menu. You will see a dialog asking "Do you want to start Outlook in Safe Mode?" — click Yes. Alternatively, press Win + R, type outlook.exe /safe, and press Enter.
If Outlook opens and works normally in Safe Mode, proceed to Fix 5 to identify and disable the problematic add-in.
Fix 2 — Repair the Office Installation
Corrupted Office installation files are a common cause of Outlook failing to open or crashing at launch.
Run Office Quick Repair
Press Win + R, type appwiz.cpl, press Enter. Find Microsoft Office or Microsoft 365 in the list. Click it, then click Change. Select Quick Repair first — this takes 2–5 minutes and fixes most installation issues without an internet connection. If Quick Repair does not resolve it, run Online Repair (requires internet, takes 15–30 minutes but is more thorough).
Fix 3 — Rebuild the Outlook Profile
A corrupted Outlook profile is one of the most common causes of Outlook not connecting to Exchange or Microsoft 365. Rebuilding it creates a fresh profile while keeping your emails on the server.
Create a new Outlook profile
Close Outlook. Press Win + R, type control panel, press Enter. Search for Mail and open it. Click Show Profiles, then Add. Give the new profile a name, add your email account, and set it as the default profile. Open Outlook and test. If it works, the old profile was corrupted — you can delete it from the same Mail settings panel.
Fix 4 — Clear the AutoDiscover Cache
Outlook uses AutoDiscover to find your Exchange/M365 server settings. A stale or corrupted AutoDiscover cache can prevent Outlook from connecting even with correct credentials.
Delete AutoDiscover registry entries
Close Outlook. Press Win + R, type regedit, press Enter. Navigate to: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover (adjust the version number for your Office version). Delete the key for your email domain. Restart Outlook — it will re-detect the server settings automatically.
Fix 5 — Fix "Outlook Not Responding" by Disabling Add-Ins
Third-party add-ins — PDF converters, CRM integrations, security tools, and email schedulers — are the most common cause of Outlook hanging or crashing.
Disable add-ins one by one
In Outlook, go to File > Options > Add-Ins. At the bottom, in the Manage dropdown, select COM Add-ins and click Go. Uncheck all add-ins and click OK. Restart Outlook. If it works, re-enable add-ins one at a time and restart after each until you identify the culprit.
Need This Fixed Right Now?
IT Cares fixes this remotely in 30 minutes or less — from $59. No fix = no charge.
Fix 6 — Fix "Cannot Connect to Server" (Exchange / Office 365 Settings)
If Outlook shows "Disconnected" or "Trying to connect..." persistently, the issue is usually authentication or server configuration.
- Sign out and re-authenticate: Go to File > Office Account > Sign Out, then sign back in with your Microsoft 365 credentials
- Check credential manager: Press
Win + R, typecontrol /name Microsoft.CredentialManager, press Enter. Remove any saved Outlook or Microsoft credentials and let Outlook re-authenticate - Verify server settings: Go to File > Account Settings > Account Settings, click your account, then Change to verify server address and port numbers match your IT administrator's specifications
- Check for MFA requirements: If your organization recently enforced multi-factor authentication, your legacy Outlook connection may be blocked — an app password may be needed
Fix 7 — Fix OST/PST File Corruption with scanpst.exe
Outlook stores your emails locally in an OST (offline) or PST (personal archive) file. If this file becomes corrupted — due to improper shutdown, disk errors, or oversized files — Outlook may fail to open or sync.
Run the Inbox Repair Tool (scanpst.exe)
Close Outlook. Find scanpst.exe — it is typically located at C:\Program Files\Microsoft Office\root\Office16\ (path varies by Office version). Open it, browse to your OST/PST file (usually in C:\Users\[username]\AppData\Local\Microsoft\Outlook\), and click Start. If errors are found, check Make a backup of scanned file before repairing and click Repair.
Fix 8 — Check Microsoft 365 Service Status
Before spending more time troubleshooting, always confirm there is not a live Microsoft service incident:
- Visit admin.microsoft.com (if you are an admin) and check the Service Health dashboard
- Visit downdetector.com/status/office-365 for user-reported outage data
- Check the @MSFT365Status Twitter/X account for real-time Microsoft incident updates
Fix 9 — Recreate the Outlook Data File
If scanpst cannot repair the OST/PST file, or if the file is too large (over 50 GB), delete it and let Outlook recreate it:
- Close Outlook completely
- Navigate to
C:\Users\[username]\AppData\Local\Microsoft\Outlook\ - Rename the
.ostfile to.ost.bak(do not delete it yet — keep it as backup) - Open Outlook — it will create a new OST file and re-sync everything from the server
- For Microsoft 365 and Exchange accounts, all email lives on the server, so nothing is lost in this process
Fix 10 — Reinstall Outlook
If all else fails, a clean reinstallation of Office resolves deeply embedded corruption that repair tools cannot address.
Uninstall and reinstall Office
Download the official Microsoft Support and Recovery Assistant (SaRA) from aka.ms/SaRA — this tool uninstalls Office completely including registry entries and hidden files. Then download and reinstall Office from portal.office.com. This takes 20–40 minutes but is the nuclear option that resolves every installation-level issue.
Need This Fixed Right Now?
IT Cares fixes this remotely in 30 minutes or less — from $59. No fix = no charge.
Frequently Asked Questions
Outlook disconnects most commonly due to: unstable internet, incorrect Exchange or M365 server settings, an expired OAuth token, a corrupted Outlook profile, or an OST file that has grown too large. Start by checking your internet, then try rebuilding the Outlook profile.
Yes — the vast majority of Outlook problems are software-related and can be fully diagnosed and resolved through a remote session. IT Cares technicians connect via AnyDesk and can repair profiles, rebuild data files, fix Exchange connectivity, and resolve crashing issues without any on-site visit.
Outlook Safe Mode starts the application with add-ins disabled and minimal configuration. If Outlook works in Safe Mode but not normally, the problem is almost certainly a third-party add-in. Hold Ctrl while clicking the Outlook icon, or run outlook.exe /safe from the Run dialog.
Sync issues are usually caused by: a disconnected Exchange/M365 account needing re-authentication, a corrupted OST file, an oversized mailbox exceeding the OST size limit, incorrect sync settings, or a Microsoft 365 service outage. Check the M365 service status dashboard first, then try rebuilding the Outlook profile.
Yes. IT Cares provides remote support for all Microsoft 365 products including Outlook, Teams, SharePoint, OneDrive, and Exchange Online for both individual and business plans. Call (888) 711-9428 or book online for same-day assistance.
Comments
Fix 3 (profile rebuild) solved our Exchange sync issue that had been driving the whole team crazy for two weeks. Our Outlook was stuck at "Trying to connect" even though internet was fine. Rebuilt the profile in about 10 minutes and everything synced immediately. Should have tried this first before calling our old IT company who charged us an hour of billable time to arrive on site and do the same thing.
My Outlook was crashing every single time I clicked on any email. Tried Safe Mode and it worked fine — so I knew it was an add-in. Disabled everything and re-enabled one by one: it was the Adobe Acrobat PDF add-in causing it. Disabled that one add-in and Outlook has been perfect for 3 weeks. Such a simple fix once you know where to look. Thank you!
Leave a Comment