How do I PERMANENTLY disable Outlook from being a default email viewer?

I've seen the answer concerning resetting the default email viewer to become the native Mac Mail app.  It did not help.

Some history:

  I decided to transition from regular Outlook 2011 use to Mail use when I encountered the following error using Outlook:

Error -17997 - database could not be rebuilt

Mail runs fine on my Mac, and for at least the last 24 hours I have used it exclusively to read and write emails that have recently arrived.  Outlook, on the other hand, cannot run more than 5 seconds without crashing -- nor do I want to run it.

I have been able to set preferences as follows:

Run Mail:

Preferences -> General ... Set 'Mail' as default

Run Outlook:

Preferences -> Default Application ... Box is unchecked "... email, contacts and calendar"

Rebooted the Mac

Now, when I try to access files of type *.eml, it _attempts_ to run Outlook (with a crash 5 seconds later).  I can use the context-sensitive menu when right-clicking the *.eml, but I have to use Mail as the _second_ menu choice, and it is quite tedious.

One of the technicians at the local Microsoft Answer Desk laid his hands on the Mac, and seemed to effectuate a fix using a p-list somewhere.  However, online, I see that Mircosoft Answers only recommends removing 

com.apple.mail.plist.lockfile

which still results in no fix for the Outlook-defaulting-as-reader.

Help.