How are you magnifying the subjects on screen? Are you using the browser font setting to increase the size? Or are you holding ctrl and then using the + key?
I believe at 400 times the entire screen would be filled with one letter, so are you using an external magnifier? Can you try using the method I described above (holding ctrl and pressing +) and seeing if the subject line still appears blurry? If so can you take a screenshot so we can take a look?