Q: blank emails

Hello!

You should try trashing the envelope index files. I'll explain below. Please make a back-up of your computer first, preferably with Time Machine: Mac Basics: Time Machine backs up your Mac - Apple Support

To trash the envelope index files (and re-index your mail file):

1. Quit Mail if it's open, preferably via the menu "Mail > Quit Mail"
2. Open the Finder and using the menu "go > go to folder" navigate to this location including the ~

~/library/mail/v2/maildata/

I suggest you simply copy-paste the line above and press the [go]-button.

    3. Once inside the folder, trash all files starting with the words envelope

    4. Once trashed, restart your OS X and open Mail. It will want to import your mails. This is expected. Please do so.

See this screenshot for visual aid:

Issue solved?