cannot open outlook classic

Question

I changed my password for my outlook.com email and now I cannot open outlook classic for my @optusnet.com.au accout. I need to use outlook calssic to convert my .ost file to .pst

Answer 1

Hi Max Gonella,

I understand you are asking how to open a support case because Outlook is still not opening or working as expected.

Please note that this is a user-to-user forum, so contributors here cannot access your account, device, or open a Microsoft support case on your behalf.

Before you contact support, could you please confirm whether you have already tried the suggestions in the AI answer above? For example, did you try opening classic Outlook in Safe Mode or checking whether the issue is related to the local Outlook data files? This helps avoid repeating steps that you have already tried.

Also, the Microsoft 365 Admin portal support option is mainly for Microsoft 365 business or school tenants, and it is usually available only to a tenant admin. If you are using a personal Outlook.com, Hotmail, Live, MSN, or Outlook for Home account, you can try contacting Microsoft Support through live chat instead:

1. Visit the Microsoft Support contact page: Contact - Microsoft Support  
2. In the search bar provided on the page, type "Outlook issue" and press Enter.  
3. Click on the "Get Help" button that appears.  
4. Scroll down the page until you see and click on the "Contact Support" option.  
5. When prompted to select your product or service, choose "Other Products".  
6. For the category, choose "Outlook".  
7. Look for and click on "Chat with a support agent in your web browser".  
8. Confirm your personal email when prompted - this is the email Microsoft will use to communicate with you during and after the support session.  
9. Explain your situation clearly: Be concise but provide all the relevant details.    

To better understand the issue here if there is any message shown when opening Outlook, please share the exact wording, but remove any email address or personal information before posting.

I hope this helps clarify the correct support path and helps you move forward with the Outlook issue.

Answer 2

Changing the Outlook.com password should not prevent classic Outlook from opening for an unrelated @optusnet.com.au account, and classic Outlook is required if the goal is to work with .pst/.ost files alongside new Outlook.

If classic Outlook will not open at all (crashes, safe mode loop, or “cannot start Outlook” type errors), the documented guidance is:

1. If Outlook shows a Safe Mode loop or crashes immediately after opening, check whether this matches the known incident described in “Classic Outlook crashes and opens in Safe Mode starting March 12 2026” and install the upcoming or already released fix when it appears in Windows Update.
2. If Outlook reports it cannot start or cannot open the Outlook window due to Exchange logon issues, this may match the “Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed.” case. In that situation, the only resolution is to open a support case from the Microsoft 365 Admin portal so Exchange Online support can request a service-side change; as a temporary workaround, Outlook on the web or new Outlook for Windows can be used.
3. If Outlook fails to open after file moves or corruption of Outlook-related files, move the .ost files from their profile path (for example, from C:\Users\{username}\AppData\Local\Microsoft\Outlook\) to a neutral location such as the desktop, then try starting Outlook again so it can recreate the necessary files.

To work with .pst files in new Outlook, classic Outlook must be installed and must match the same 32-bit or 64-bit architecture. Once classic Outlook is working again, .pst files can be opened via File → Open & Export → Open Outlook Data File in classic Outlook, or via Settings → Files → Outlook Data Files → Add file in new Outlook (with the architecture and installation requirements met).

If classic Outlook is not installed on the device (for example, only new Outlook is present and the “go back to classic Outlook” button does nothing), install classic Outlook using the documented Microsoft Store link and then retry opening Outlook and working with .pst files.

If none of these documented cases match the exact behavior, or if Outlook still cannot be opened after trying the file move and update steps, the next step is to open a support case so that Outlook/Exchange support can investigate the specific profile and account configuration.

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References:

• Error when opening classic Outlook: "Cannot start Microsoft Outlook. Cannot open the Outlook window. The set of folders cannot be opened. The attempt to log on to Microsoft Exchange has failed."
• What if Outlook can not open after the failure of transferring Outlook related files?
• Go back to classic Outlook button not working correctly in new Outlook
• Open and find items in an Outlook Data File (.pst)
• Open and close Outlook Data Files (.pst)
• Outlook won't open, says it coundn't open last time and asks if I want to open in Safemode - Microsoft Q&A
• Class outlook is not working properly after Windows 11 version 25H2 update - Microsoft Q&A
• Outlook Classic not opening properly or recording sent mails after 2026-01 Security Update (KB5074109) (26200.7623) - Microsoft Q&A