Outlook saying Trying to connect or Disconnected in the status bar is one of those tickets where the fix is usually simple but the possible causes are many. Service outage, expired token, broken profile, a bad add-in, a corrupt OST file, or a laptop that has quietly lost its network.
Work through it in this order. Each step rules out a whole class of causes, and you will avoid the classic mistake of rebuilding the profile when the real problem was a Microsoft 365 incident.
Rule out the obvious first
Ask the user to open Outlook on the web at outlook.office.com. If that works, the mailbox and the account are fine and the problem is the desktop client or the machine. If the web version also fails, check the Microsoft 365 service health page in the admin center before anything else. An Exchange Online incident looks exactly like a broken laptop from the user's side.
Look at the bottom of the Outlook window. Working Offline means someone clicked the button under Send/Receive, and it stays clicked until unclicked. Need Password means the token expired and the sign-in prompt got dismissed or blocked. Disconnected means the client tried and failed. Each one sends you somewhere different.
Read the connection status window
Hold Ctrl and right-click the Outlook icon in the system tray, then choose Connection Status. Every connection to Exchange is listed with its server name, protocol, status and request counts. Healthy rows say Established. Rows that stay at Connecting or show growing failure counts tell you the client is reaching out and not getting through, which is usually network, proxy or authentication.
The same menu has Test E-mail AutoConfiguration. Untick Guessmart and Secure Guessmart, tick Use Autodiscover, enter the user's address and password and run it. If Autodiscover fails, Outlook cannot find the mailbox settings and will never connect. Common reasons are a stale autodiscover DNS record pointing at an old on-prem server, or a proxy that blocks the autodiscover endpoints.
Credential and token problems
Modern authentication in Outlook uses tokens that are refreshed silently. When that breaks, Outlook either loops on a sign-in prompt or sits at Trying to connect without asking. Start by removing stale entries: open Control Panel > Credential Manager > Windows Credentials and delete anything starting with MicrosoftOffice16_ or ADAL. Then sign out of Office from File > Office Account and sign in again.
If that does not do it, check the Entra ID sign-in logs for the user. A Conditional Access policy that requires a compliant device or blocks legacy protocols will fail the sign-in silently in the client, and the log tells you exactly which policy did it. An expired password, a disabled account or a recently revoked session shows there too.
Get-MgUser -UserId jsmith@contoso.com -Property AccountEnabled, LastPasswordChangeDateTime | Format-ListProfile and OST repair
When the account and network are fine but Outlook still will not connect, the profile or the cached data file is the next suspect. Start Outlook in safe mode to rule out add-ins. If safe mode connects, an add-in is the cause: disable them in File > Options > Add-ins and re-enable one at a time.
For the OST, close Outlook, go to %localappdata%\Microsoft\Outlook and rename the .ost file. Outlook rebuilds it on the next start. This is safe for Exchange and Microsoft 365 mailboxes because the server holds the data, but tell the user it will take a while to download and that search will lag until indexing catches up. If none of that works, create a new profile from Control Panel > Mail > Show Profiles > Add, and set it as the default.
- Close Outlook and run it in safe mode with the command below.
- If it connects, disable add-ins and restart normally.
- If it still fails, rename the OST file and start Outlook.
- If it still fails, create a new mail profile and test with that.
outlook.exe /safeAdd-ins, antivirus and the new Outlook
Security software that scans mail traffic can sit between Outlook and Exchange and break the connection after an update. If the machine has a mail-scanning antivirus plugin, disable that feature for a test. Web proxies that inspect TLS need the Microsoft 365 endpoints excluded; Microsoft publishes the list and it changes.
Finally, the new Outlook for Windows is a separate application with its own behaviour. If the user was switched by the toggle in the corner and things stopped working, the toggle goes back the other way. Support both, but note in the ticket which client the user is on so the next tech does not troubleshoot the wrong one.
Frequently asked questions
Outlook connects but new mail only arrives when I click Send/Receive. Why?
Usually the cached mode connection dropped and reconnected in a degraded state, or the mailbox is in Online Mode over a slow link. Restart Outlook first. If it repeats, check for an add-in or a proxy that interrupts the long-lived connection.
Is it safe to delete the OST file?
Yes for Exchange and Microsoft 365 accounts, because the mailbox lives on the server. It is not safe for POP accounts or for PST files, which are the only copy. Rename rather than delete so you can go back if needed.
Why does Outlook keep asking for the password?
A stale credential in Credential Manager, a Conditional Access policy the device does not meet, or basic authentication being attempted against a tenant that has it disabled. Clear the credentials, then check the sign-in log for the real reason.
Takeaway
Check Outlook on the web and service health before you touch the client, then read the connection status window instead of guessing. Clear stale credentials, test in safe mode, and only rebuild the OST or the profile when the cheaper steps have been ruled out. Most Trying to connect tickets are resolved before you get that far.