How to set all Outlook contacts to "Let Outlook decide the best sending format"

Running Outlook 2010.  Somehow about 1/3 of my Contacts have their Internet Format set to: "Send using Outlook Rich Text Format".  My guess is that these are the ones that I imported from other applications over the years.  I have thousands of Contacts, and many of the Contacts have multiple email addresses, so it would take forever to edit all of them by hand.  How can I change the Internet Format of all of my Contacts' email addresses to be "Let Outlook decide the best sending format" - en masse?

Thanks in advance for your help!
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JohnBusiness Consultant (Owner)Commented:
I am in Outlook 2010 now. It has been a long time since I ever changed the "best format" for my email, I looked through all the Outlook options and could not see this option any more. Where do you see the option in Outlook 2010?  

Thanks, ... Thinkpads_User
whc4Author Commented:
Open an Outlook Contact.

Double-click the person’s email address within the contact.  This will bring up a small window that is sort of a condensed version of the Contact.

Click on the small Notebook-looking icon on the condensed Contact card and choose “Outlook Properties”.

Notice the “Internet Format” drop-down box on the resulting “Email Properties” dialog box.
JohnBusiness Consultant (Owner)Commented:
Thanks. That option is a long way down which is why I did not see it. I have contacts in my Outlook 2010 that came originally from Outlook Express a decade ago and they all appear to be set to "Let Outlook Decide". I did some googliing around and it appears this is entirely an individual option by contact (which you knew) and there does not appear to be a way to change the property en masse. It appears to override the main option to use text or HTML for sending mail.

I shall continue to look and meanwhile, perhaps someone else know how to do this.

... Thinkpads_User
JohnBusiness Consultant (Owner)Commented:
I have pretty much confirmed that this option is completely individual by contact. The closest article I could find is this one, but it has no answer.

... Thinkpads_User

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JohnBusiness Consultant (Owner)Commented:
Probably my last gasp.  You can export the contacts into an Excel file (which means you can import them), but that option is not there that I can see. There is an email type, but all mine are just SMTP.

.. Thinkpads_User
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