Fix Cannot open Outlook window. The file .ost cannot be accessed, You must connect to Microsoft Exchange before you can use Outlook data file.

Outlook needs to be connected with the server to send & receive emails. If Microsoft Outlook cannot connect to the server, see this post.

Microsoft 'deploying fix' after users report problems with Outlook and Teams The issue is thought to have started around 8am. More than 80% of reported problems involved Outlook, when the email ...

The inability to connect from a Vista PC to an Exchange Server may be due to a conflict with the Windows Firewall.