What we're all experiencing is seeing the source code of selected emails rather than the regular display. From what I've read online, MS is well aware of the problem but do not seem to be incentivized to provide a fix.
It's a debilitating problem since some of these emails are from financial institutions. I've not been able to ascertain any specific category of emails (spam, unsolicited offers, etc.) this is occuring with.
Needless to say, it's a problem begging for a solution!