How to Fix New Outlook for Mac Not Working
Why New Outlook for Mac Breaks , And Why Microsoft's Error Messages Don't Help
I've seen this exact situation play out on dozens of Mac deployments: you open the new Outlook for Mac, and something's just broken. Maybe the navigation pane (what Microsoft calls the folder tree or TOC , the left-side Table of Contents panel that lists your Inbox, Sent, Calendar, and all your folders) is completely blank. Maybe Outlook refuses to load your email at all. Maybe it crashes on launch, throws up a vague spinning wheel, or gets stuck on "Loading…" forever. You haven't changed anything. It just decided to stop working.
I know how frustrating that is, especially when email is the first thing you need the moment you sit down to work.
The new Outlook for Mac is a fundamentally different beast from the legacy version. Microsoft rebuilt it from scratch using a web-based rendering engine rather than native macOS AppKit components. That's why it looks similar to Outlook on the web, because, under the hood, it basically is. This architectural shift introduced a whole new class of failure modes that the old Outlook never had: corrupted local SQLite cache databases, OAuth token expiration loops, broken add-in sandboxes, macOS Keychain conflicts, and WebView2-style rendering failures that leave your folder panel (the TOC sidebar) empty or unresponsive.
The new Outlook's TOC, the left-side navigation column showing Favourites, your account folders, Shared Mailboxes, and Groups, is one of the most frequently broken parts of the app. When the local sync database gets out of sync with the server, or when the app's identity token expires mid-session, the TOC simply fails to populate. You'll see folder names disappear, the Inbox badge count showing emails you can't access, or a completely grey sidebar with no folders visible at all. Microsoft's error UI in these cases is spectacularly unhelpful: usually just a generic "Something went wrong" banner with a Retry button that loops forever.
The root causes fall into a few distinct buckets. First, profile corruption, the new Outlook stores your account data in a SQLite database under ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/, and this database regularly gets corrupted after forced shutdowns or macOS updates. Second, macOS Keychain conflicts, Outlook stores OAuth refresh tokens in Keychain, and after a password change or an IT-enforced policy reset, stale tokens block new authentication. Third, app cache bloat, the new Outlook's WebKit rendering cache can balloon to several gigabytes and starts causing rendering failures when it does. Fourth, Microsoft 365 service-side issues, sometimes it's not your Mac at all; it's the Exchange Online endpoint your tenant connects to.
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The Quick Fix, Try This First
Before you spend an hour digging through logs, try this. It fixes the new Outlook for Mac TOC and loading issues in about 60% of cases.
Force-quit Outlook and clear the main cache folder. Here's exactly what to do:
- Press Cmd + Q to quit Outlook. If it's frozen, press Cmd + Option + Esc, select Microsoft Outlook, and click Force Quit.
- Open Finder, click the Go menu in the menu bar, then hold Option, the Library folder will appear. Click it.
- Navigate to
Containers > com.microsoft.Outlook > Data > Library > Caches - Select everything inside the
Cachesfolder and move it to Trash. Don't delete the folder itself, just its contents. - Also go to
~/Library/Group Containers/UBF8T346G9.Office/and look for a folder namedOutlook TemporOutlook Staging. Move those contents to Trash too. - Relaunch Outlook. It will rebuild its local cache from scratch, which takes 1–3 minutes depending on mailbox size.
If your TOC sidebar was blank or your folder list was missing, this rebuild almost always restores it. You'll see a progress indicator as it re-syncs your folder hierarchy from Exchange Online. Give it a full 5 minutes before concluding it hasn't worked.
outlook.office365.com or substrate.office.com, these are the endpoints the new Outlook hits to rebuild its TOC.
If the cache clear didn't restore your TOC or fix the loading issue, the next step is to remove and re-add your account. This forces Outlook to tear down the corrupted account identity and rebuild it from scratch, including generating fresh OAuth tokens from Microsoft Entra ID (formerly Azure AD).
Go to Outlook menu > Settings (or press Cmd + ,). In the Settings panel, click Accounts. You'll see your email accounts listed. Select the affected account and click the minus (−) button at the bottom left of the accounts list. Outlook will warn you that removing the account deletes locally cached data, that's exactly what you want. Click Delete.
Now close Settings and restart Outlook completely. When it relaunches, go back to Settings > Accounts and click the plus (+) button. Choose New Email Account and enter your Microsoft 365 email address. Outlook will redirect you through the Microsoft sign-in flow in a browser window, sign in with your full credentials, complete any MFA prompts, and click Accept on the permissions consent screen.
Once the account is re-added, Outlook will rebuild the TOC from your Exchange Online mailbox. Watch the sidebar, you should see folder names begin populating within 30–60 seconds. If your Inbox, Drafts, Sent, and custom folders all appear, you're done. Event log equivalent: if you check Console.app and filter for com.microsoft.Outlook, you should stop seeing OAuthTokenRefreshFailed entries.
The new Outlook for Mac stores Microsoft 365 authentication tokens in macOS Keychain. After a password change, MFA method change, or conditional access policy update pushed by your IT team, those old tokens don't get cleaned up automatically. They sit in Keychain, Outlook tries to use them, the authentication fails silently, and your TOC and inbox stop loading, all with no useful error on screen.
Open Keychain Access, press Cmd + Space, type "Keychain Access", and press Enter. In the search bar at the top right, type Microsoft. You'll likely see dozens of entries. Look specifically for entries named:
Microsoft Office Identities Cache 2
Microsoft Office Identities Settings 2
com.microsoft.adalcache
com.microsoft.identity.universalstorageSelect each of these entries and press Delete. Keychain will ask for your Mac login password to authorize the deletion, enter it and click Allow. Delete all of them. Don't worry about deleting too much here; Outlook will recreate all of these on next launch after you sign back in.
After clearing Keychain, force-quit Outlook and relaunch it. You'll be prompted to sign in again. Complete the sign-in flow including any MFA. Once authenticated, Outlook gets a fresh set of OAuth tokens, no more stale credential conflicts. This fix is especially effective if you recently changed your Microsoft 365 password, your company enforced a new conditional access policy, or your IT team migrated accounts between tenants.
The new Outlook for Mac maintains a profile SQLite database that tracks your folder structure, account configuration, and sync state. When macOS crashes, when you force-quit Outlook during a sync, or after certain macOS updates, this database can get corrupted. The symptom is almost always the same: Outlook launches, the TOC sidebar appears but shows nothing, or it shows your account name but no folders underneath it.
To rebuild the profile database, you'll use the built-in Outlook Database Utility. Quit Outlook first. Then open Finder, press Cmd + Shift + G, and enter this path:
/Applications/Microsoft Outlook.app/Contents/SharedSupport/Look for Outlook Database Utility.app and double-click it. Select your profile (usually named "Main Profile" or your email address) and click Rebuild. The utility will verify the database integrity, repair inconsistencies, and rebuild the folder index. This process can take anywhere from 2 minutes to 20 minutes depending on mailbox size, do not interrupt it.
When it finishes, it will report either "Rebuild Successful" or flag any errors it couldn't repair. If the rebuild completes successfully, relaunch Outlook. Your TOC should populate normally. If the utility reports it cannot repair the database, proceed to creating a new profile: in the Database Utility, click Create New Profile, give it a name, set it as the default, then relaunch Outlook and re-add your account.
The new Outlook for Mac has a toggle that switches between the legacy Outlook experience and the new web-based engine. If you're experiencing TOC failures that none of the above steps fixed, it's worth testing whether the issue is specific to the new engine, and whether temporarily switching back reveals any diagnostic information.
In Outlook, look at the top-right corner of the window for the "New Outlook" toggle switch. Click it to switch back to legacy Outlook. When prompted, click Continue. Outlook will restart in legacy mode.
In legacy mode, check if your folder TOC and Inbox load correctly. If they do, you've confirmed the issue is with the new Outlook engine specifically, not your account or the Exchange server. If legacy Outlook also has empty folders, the problem is likely Keychain or profile-level corruption (go back to Steps 2 and 3).
To switch back to new Outlook, click the "New Outlook" toggle again and select Switch Back to New Outlook. Before doing so, try this trick I've seen resolve persistent TOC failures: while in legacy Outlook, go to Tools > Accounts, select your account, and click Advanced. Under the Server tab, verify that the Exchange server field is set to outlook.office365.com and not a stale on-premises Exchange address. A stale server address here carries over into new Outlook and causes exactly the empty-TOC symptom you're fighting.
Once verified, switch back to new Outlook. Allow a full 3–5 minutes for the initial sync to complete before deciding whether the fix held.
If you've tried everything above and the new Outlook for Mac TOC still won't load, the app installation itself may be damaged, or you're running an outdated build with a known sync bug that's already been patched.
First, check your Outlook version: go to Help > Check for Updates in the menu bar. Microsoft AutoUpdate will open. Click Update All and let it install any pending Outlook updates. As of early 2026, the new Outlook for Mac build 16.94 and later includes fixes for several TOC rendering failures that affected builds in the 16.88–16.91 range. Make sure you're on the latest.
If you're already up to date, perform a full app reset via Terminal. This is the nuclear option short of a complete reinstall, it wipes all app-level preferences and forces Outlook to rebuild from a clean state:
# Quit Outlook first, then run these commands one at a time:
defaults delete com.microsoft.Outlook
rm -rf ~/Library/Containers/com.microsoft.Outlook
rm -rf ~/Library/Group\ Containers/UBF8T346G9.Office/Outlook
rm -rf ~/Library/Application\ Support/Microsoft/Office365/User\ Content.localizedAfter running these commands, relaunch Outlook. It will behave exactly like a fresh install, you'll need to sign in and re-add your account. This resolves even deep preference corruption that the Database Utility can't touch. After re-signing in, wait 5–10 minutes for the full folder hierarchy to sync. Your TOC should now be fully populated and functional.
Advanced Troubleshooting
If you're an IT admin troubleshooting the new Outlook for Mac TOC issue across multiple machines, or if you're dealing with a domain-joined Mac in an enterprise environment, here's what to look at beyond the standard user-level fixes.
Check macOS Console Logs for Specific Error Codes
Open Console.app from /Applications/Utilities/. In the search bar, filter for com.microsoft.Outlook and set the timeframe to "Last 5 Minutes" after reproducing the TOC failure. The errors that matter most are:
EWSError: ErrorItemNotFound, Exchange Web Services can't find the root folder; usually a mailbox migration artifactSyncStatus: FolderHierarchySyncFailed, the folder hierarchy sync specifically is failing, distinct from message syncOAuthError: AADSTS700082, refresh token expired; Keychain cleanup (Step 2) is the fixOAuthError: AADSTS50076, MFA required but not completing; check conditional access policiesCoreData: fault: Serious application error, SQLite database corruption; rebuild profile (Step 3)
MDM-Managed Macs and Configuration Profile Conflicts
On Macs managed via Jamf Pro, Intune, or another MDM solution, Microsoft 365 configuration profiles sometimes inject account settings that conflict with how the new Outlook authenticates. Specifically, if your MDM deploys a configuration profile with com.microsoft.Outlook keys that set DefaultEmailAddressOrDomain to an on-premises domain while the actual mailbox is in Exchange Online, the TOC will load an empty folder hierarchy from the wrong endpoint.
Check active configuration profiles on the Mac: open System Settings > Privacy & Security > Profiles. Look for any profile with "Outlook" or "Office" in the name and examine what keys it's deploying. If you see Exchange server settings pointing to an on-premises FQDN for a cloud-only mailbox, that profile needs to be updated in your MDM console.
Network-Level: Allow Required Microsoft 365 Endpoints
The new Outlook for Mac's TOC relies on the substrate.office.com endpoint for folder hierarchy sync, this is different from the classic EWS endpoint. If your organization's proxy or firewall is blocking *.substrate.office.com, *.office365.com, or *.outlook.com on port 443, the TOC will fail silently. Run a quick connectivity test from Terminal:
curl -I https://substrate.office.com
curl -I https://outlook.office365.com/EWS/Exchange.asmxBoth should return HTTP 200 or 302. If either returns a connection error or a proxy interception certificate warning, work with your network team to add these endpoints to the allowlist. Microsoft publishes the full list of required URLs in the Microsoft 365 URLs and IP address ranges documentation.
Event Viewer Equivalent: Unified Logging on macOS
For deeper log analysis, use the log command in Terminal to stream Outlook-specific logs with full verbosity:
log stream --predicate 'subsystem == "com.microsoft.Outlook"' --level debugReproduce the TOC failure while this is running. Look for folderSync, hierarchyRequest, and tokenRefresh entries, these will tell you exactly at which stage the new Outlook for Mac is failing.
EWSError: ErrorInternalServerError repeatedly, which indicates a server-side issue with your Exchange Online mailbox rather than anything wrong with your Mac. Contact Microsoft Support and open a ticket under the Microsoft 365 > Exchange Online category. Have your tenant ID ready (find it in the Microsoft 365 admin center under Settings > Org Settings > Organization Profile) and include exported Console logs from the time of the failure, this dramatically speeds up resolution.
Prevention & Best Practices
Once you've fixed the new Outlook for Mac TOC issue, the last thing you want is to go through all of this again in two weeks. Here's how to keep the new Outlook running cleanly.
Keep Outlook updated via Microsoft AutoUpdate. Microsoft ships bug fixes for the new Outlook for Mac roughly every two weeks. Many TOC sync failures that appear in a particular build are silently patched in the next release. Set AutoUpdate to install updates automatically: open Microsoft AutoUpdate, go to Preferences, and set the update mode to Automatically Download and Install. Don't let Outlook fall more than two releases behind.
Never force-quit Outlook during an active sync. The new Outlook for Mac writes its SQLite profile database during folder sync operations. Killing the process mid-write is the single most common cause of database corruption that leads to empty TOC on next launch. If Outlook appears frozen, wait at least 60 seconds before reaching for Force Quit. If you must force-quit, the Database Utility rebuild (Step 3 in this guide) takes only a few minutes and is worth running proactively afterward.
Manage your mailbox size. The new Outlook for Mac slows dramatically and becomes prone to TOC sync failures when a mailbox exceeds roughly 50,000 items in the primary folders. Archive older emails regularly: in Outlook, go to Tools > Archive and move anything older than one year to an archive mailbox or a local .olm archive. A leaner mailbox means faster, more reliable folder hierarchy syncs.
Don't install untrusted add-ins. Third-party Outlook add-ins that load into the new Outlook for Mac can inject JavaScript into the rendering engine and interfere with TOC rendering. Only install add-ins from the Microsoft AppSource marketplace or from vendors explicitly approved by your IT team. If a TOC issue started immediately after installing a new add-in, disable it: go to Tools > Get Add-ins, click My Add-ins, and toggle off any recently installed ones.
- Enable automatic updates in Microsoft AutoUpdate, never run a build more than 4 weeks old
- Restart Outlook fully (not just minimize it) once a week, this clears in-memory cache build-up that leads to TOC slowness
- After any macOS system update, launch Outlook and give it 10 minutes to re-sync before assuming something is broken
- If your company recently changed conditional access or MFA policies, proactively clear Keychain entries (Step 2) before Outlook breaks
Frequently Asked Questions
Why is my new Outlook for Mac folder list completely empty after a macOS update?
macOS updates, especially major version upgrades like Ventura to Sonoma or Sonoma to Sequoia, frequently invalidate the sandboxed container permissions that Outlook uses to access its profile database and Keychain entries. After a major macOS update, always do a full Outlook restart first, then wait 5 minutes for re-sync. If the TOC is still empty, the fastest fix is clearing the Keychain entries for Microsoft Office Identities Cache 2 (Step 2 in this guide) followed by signing back in. This happens because macOS regenerates certain container security identifiers during the upgrade, breaking Outlook's access to its cached authentication tokens.
New Outlook for Mac keeps saying "Loading" forever, how do I stop it?
A permanent "Loading" state in the new Outlook for Mac almost always means it's stuck in an OAuth token refresh loop, it's trying to authenticate to Exchange Online, failing silently, and retrying in a loop. The quick check: open Console.app, filter for com.microsoft.Outlook, and look for repeated OAuthTokenRefreshFailed or AADSTS700082 entries. If you see those, go straight to Step 2 in this guide, clear your Microsoft Office Keychain entries, force-quit Outlook, and sign back in fresh. A corporate VPN that's only partially connected can also cause this, so try toggling your VPN off and back on before anything else.
My Outlook TOC shows folder names but clicking them does nothing, why?
This is usually a WebKit rendering issue specific to the new Outlook's web-based engine. The folder names are being rendered from a partially loaded local cache, but the click handlers aren't wired up because the JavaScript that runs the TOC interaction failed to initialize. The fix is to clear the app's WebKit cache: quit Outlook, delete the contents of ~/Library/Containers/com.microsoft.Outlook/Data/Library/Caches/, then relaunch. If that doesn't work, check if you have any browser extensions or privacy tools installed that might be intercepting WebKit network requests, some macOS privacy tools inject themselves into WebKit contexts, including the one Outlook uses.
Can I go back to the old Outlook for Mac permanently?
As of 2026, Microsoft has made the new Outlook for Mac the default and the legacy version is in maintenance-only mode, meaning it still exists but no longer receives feature updates. You can switch back using the "New Outlook" toggle in the top-right corner of the app window, and you can stay on legacy as long as your Microsoft 365 tenant policy allows it. However, Microsoft has signaled that the legacy version will be retired; some enterprise tenants have already lost the ability to opt out via Group Policy (GPO equivalent: the NewOutlookForMacEnabled preference key). If you need to stay on legacy for a specific workflow, check with your IT admin about whether the NewOutlookDefault MDM key is deployable in your environment.
Why do shared mailboxes disappear from the Outlook for Mac TOC randomly?
Shared mailboxes in the new Outlook for Mac have a known intermittent sync issue where they drop out of the TOC after idle periods, typically after the Mac wakes from sleep with a stale network connection. When the main account re-authenticates on wake, the shared mailbox permissions aren't always re-validated in the same request, so they briefly disappear. The fix is usually just waiting 30–60 seconds for the sync to catch up. If they don't come back, go to Settings > Accounts, expand your main account, find the shared mailbox in the list, and toggle it off and back on. If shared mailboxes disappear daily, check that the "Download shared folders" option is enabled: Settings > Accounts > [your account] > Advanced > Sync shared mailboxes.
New Outlook for Mac crashes on launch with error code 0xc0000005, what does that mean?
Error code 0xc0000005 is an access violation, the process is trying to read or write to a memory address it doesn't have permission to access. On Mac this translates to a SIGSEGV or SIGBUS crash, visible in the crash reporter as an EXC_BAD_ACCESS exception. This almost always means the Outlook container directory has incorrect permissions, often caused by a macOS Repair Disk operation or a third-party cleanup tool that reset sandbox container permissions. Open Terminal and run: chmod -R 755 ~/Library/Containers/com.microsoft.Outlook. If that doesn't resolve it, the cleanest path is the full Terminal reset in Step 5 of this guide, followed by a re-download of Outlook from the Mac App Store or from Microsoft's own download page to ensure the app binary itself isn't damaged.