I am noticing that some, not all, of my inbound emails are switching to plain text formatting vs. HTML.

Any idea why some would change and others do not? At first I thought this was the sender, but found it is definitely in Outlook as the same emails will appear fine on other devices.

I have checked all of my preferences. I have removed Microsoft pref files, and I have recently rebuilt my database (don't know if that has helped or not yet). Any ideas?

Thank you for your assistance.

OS Mavericks 10.9.2

Outlook 14.4.1