FIX:

1) Close Netscape

2) Find all files with the name *.snm

3) Edit Select-All

4) Delete and send to the recycle bin

5) Try to read the mail

If that does not work try this,

1) Close Netscape

2) Rename the corrupt mail box

3) Open Netscape and see if a new box has been created

4) Check the renamed mail box to see if the mail is readable