Error message when an Office 365 pre-upgrade user tries to open Outlook: "Unable to open your default e-mail folders"

When a Microsoft Office 365 pre-upgrade user tries to open Microsoft Outlook, the user receives the following error message:

To fix this issue, make sure that the Encrypt data between Microsoft Office Outlook and Microsoft Exchange option is selected in Outlook. To do this, follow these steps.

Outlook 2013 and Outlook 2010

1. Click File, click Account Settings, and then click Account Settings.
2. On the E-mail tab, click Microsoft Exchange, and then click Change.
3. On the Server Settings page, click More Settings.
4. On the Security tab, click to select the Encrypt data between Microsoft Office Outlook and Microsoft Exchange check box, and then click OK.
5. When you're prompted to restart Outlook, click OK.
6. Click Next, and then click Finish.
7. Click Close, and then restart Outlook.

Outlook 2007

1. In Outlook 2007, click Tools, and then click Account Settings.
2. On the E-mail tab, click Microsoft Exchange, and then click Change.
3. On the Microsoft Exchange Settings page, click More Settings.
4. On the Security tab, click to select the Encrypt data between Microsoft Office Outlook and Microsoft Exchange check box, and then click OK.
5. When you're prompted to restart Outlook, click OK.
6. Click Next, and then click Finish.
7. Click Close, and then restart Outlook.

This issue may occur because Exchange Online forces an encrypted connection between the client (Outlook) and the server.

By default, Outlook 2013, Outlook 2010, and Office Outlook 2007 "encrypts" data between client and server. Therefore, this scenario occurs only in environments in which this setting is manually overwritten.

Still need help? Go to the Office 365 Community website.