Winmail.dat Issue

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New Member
Outlook version
Outlook 2010 32 bit
Email Account (as MS Exchange)
I am having the dreaded winmail.dat problem. I have an (new 365) email account set up as an Exchange account on Outlook 2010. It has been working great up to a couple of weeks ago. Nothing has been changed on my PC as far as Outlook is concerned. I am at a loss. I have tried everything listed here...clearing the autocomplete cache...the TNEF registry thing...the settings for sending messages...checking the contacts for RTF...I have tried EVERYTHING to fix it.

After much trail and error I was able to determine what was causing (and workaround) winmail.dat problem, but I am not sure why my fix works? Here is what I did:

I copied the contacts in my's address book and pasted them into the My Outlook Data File's address book. Next I deleted all the contacts in the's address book. I then proceeded to clear the autocomplete cache and restarted Outlook. Next I sent a test html email message with a PDF attached using a contact from My Data File's address book (this email was sent to another email address of mine which I use on my iPad...Yahoo address..default iPad mail client). Guess what? No winmail.dat...just the PDF.

So I copied and pasted the contacts out of My Data File's address book back into the's address book. Then I cleared the autocomplete cache and restarted Outlook. Next I sent another email to my iPad's Yahoo email address. This time I used the contact from the address book. The dreaded winmail.dat reared its ugly head again. Just to be sure, I cleared the autocomplete cache again and restarted Outlook. Then I sent another email with the same PDF attached using My Data File's address winmail.dat.

What could be going on here? Did Microsoft change something on their end or what? Like I stated earlier, this all started about 2 weeks ago. Why would the address book cause the winmail.dat problem?

Thanks in advance!
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