Where does the Outlook Connector client store its local data cache?

On a default installation, the local data cache is stored here:-

C:\Users\[windows user]\AppData\Roaming\Alt-N\Outlook Connector 2.0\Accounts\[Outlook profile]\[email address]

Possible issues to note:

The above location may be hidden by Windows.  To show this folder, go into Tools -> Folder Options -> View in Windows Explorer and ensure that the highlighted option ‘Show hidden files and folders and drives is selected as shown below:-