Plain text emails appear in a white (invisible) font in Outlook 2013.??
Please follow these steps to resolve it!!
1.File > Options > Mail > Stationery and Fonts,
then clicking the Font button under Composing and reading plain text messages.
The font colour should normally be set to Automatic, and in our case it was inexplicably set to white. Setting it back to Automatic immediately solved the problem.
Bizarrely, even though the Font color was set to white (as shown in the above screenshot), you can see that this was not reflected in the preview on either the Font dialog or the preceding Signatures and Stationery dialog.
Hope this will work for you as well!!