Incoming mail with Squares instead of characters

["Steve Knecht" <stevek@gesn.com>]

I am getting an inordinate amount of email where characters are being displayed with

squares rather than characters.  If anyone's got this same thing and knows whats happening let me know please.  I am not getting it when I start an email thread myself, but it occurs in an email response I am typing if these characters are present in the original email.