Sharing

From the Mail menu bar, please select

Mail ▹ Preferences... ▹ General ▹ Default email reader: Mail

If you don't use Mail, you may be able to set the preference in the mail client you do use.

If Microsoft Outlook 2011 is installed and you don't want it to be the default mail reader, select

Outlook ▹ Preferences... ▹ General

Uncheck the box marked

Make Outlook the default application for e-mail, calendar, and contacts

If the default mail client resets to Mail after you have set it to something else, you may have to disable iCloud Drive temporarily before changing it.

Please follow the link in the last line of my earlier comment.

You will remove iCloud Drive documents from your computer, but not from iCloud. When you reenable iCloud Drive, the documents will be restored.

Although the problem is not the same, please follow the instructions in this support article to reset the Launch Services database.

Instead of typing the command as directed in the article, I suggest that you copy and paste it from the web page into the Terminal window. Make sure you select the whole line before copying. One way to do that is to triple-click anywhere in the line.

If you don't already have a current backup, back up all data before proceeding. You may have to log out or restart to see a change.