If you are unable to send outgoing email (but incoming email works fine) and you receive an error message that says your 'Outlook data file cannot be accessed' after upgrading either Outlook or Windows it's a sign that your profile is corrupt.

0x8004010F: Outlook data file cannot be accessed

If the text of the message says the operation failed, it could also mean a corrupt profile.

0x8004010F: The operation failed. An object could not be found

If you are using an IMAP account and have contents in folders labels "(This computer only)" export those folders to a new pst before removing the account from your profile.

The recommended fix is to create a new profile, especially if you only have one or two email accounts, in part to prevent problems with the address book. If you have multiple email accounts or just don't want to create a new profile, use the Keep Profile Method instead.

Create a New Profile

To create a new profile, close Outlook and open the Control Panel then search for Mail.

1. Open the Mail applet then click Show Profiles.
   
2. Click Add to create a new profile. After the profile is created, you can delete the old one. Does it matter if you delete the old one first? No, not as long as you use a unique new name for the profile.
   
3. Use Auto Account Setup to add the account to your profile.
   
4. If you are using POP3, after the account is added you'll want to tick the box to Change Account Setup then click Next. This will allow you to use your old pst file.
   
5. Select your old pst file then exit the dialogs. (IMAP creates a new data file.)
   
6. Before closing the Mail dialog (screenshot in step 2), delete the old profile or select the new profile in Always use this profile.
7. Restart Outlook.

Keep Profile Method

If you have a lot of email accounts and don't want to create a new profile, you can try using the following steps. If this doesn't fix the error and messages send, you'll need to create a new profile.

1. Go to File, Account Settings, Account Settings
   
2. Click Change Folder
3. Click New Outlook Data File and create a data file to use temporarily.
   
4. Enter a name for the data file, such as 'test' or 'delete-me' then click OK.
5. If the Inbox in the new temporary data file is not selected, expand the subfolders and select Inbox then click OK to close the dialog and return to Account Settings.
   
6. Click on Change Folder again
7. Re-select your data file. Expand the subfolders and select Inbox then click OK to close the dialog.
   
8. Switch to the Data Files tab and remove the temporary pst file from your profile.
   
9. Close the Account Settings dialog.

If this doesn't fix the send error, you'll need to make a new profile. Delete the temporary pst file after closing Outlook.