In case you get the error message, while trying to open your mail file using the icon on the workspace, you can dismiss the error message and close all the opened tabs of the mail file. Go to the workspace and use the icon to again open the mail file.
Notes: The 'No sitemap found' error message usually occurs when you open the mail file from the workspace, while mailbox and calendar tabs of a previous session are still open.
There are various other ways to fix such error messages and issues occurring in Lotus Notes. In case you are still not able to see mail items in the mailbox folders, you can use various techniques to recover inaccessible or lost mail items from Lotus Notes.
Since, Lotus Notes is a professional software, used mostly in organizations for an efficient communication; it is advised to use a professional tool to overcome any issue including data loss situations.
Recovery Toolbox for Lotus Notes is a highly efficient tool to recover user mailbox items like emails, contacts, notes, journals, etc. from corrupt or inaccessible Lotus Notes database files. With the ability to display preview of all the recoverable items, the tool ensures an efficient recovery process. The recovered files can be then saved in any desired location. In addition, the tool is widely compatible across various versions of Windows operating system including Windows 8, 7, Vista, Server 2003, XP, 2000, and NT (SP6).
Here the link: https://recoverytoolbox.com/lotusnotes.html