Recovery of corrupted email text bodies due to malware

On May28, 2014, our anti-virus software detected and removed malware.  During that time all of our current emails and emails in all folders became unreadable.  Once the malware was removed, new emails were fine, but previous emails are still unreadable.  The email headers are fine however, just the body of the emails appear to be corrupt (jibberish and special characters).  Is there a way to decrypt the emails to return them to normal?