Recieved messages have "None" in the "From" Field
 

I've seen a number of people who couldn't send messages due to a similar
problem.

A whole string of my emails (recieved) no longer have anyone in the "From"
Field, although they do have dates in the "Date" Field. When I double-click
the message, it opens and shows me the "From" Field, but then the "Date"
Field is blank.

This just happened, spontaneously, I believe.

Thanks in advance,

Will Stewart