The RedHat 6.0 and 6.1 /bin/mail dums core when the mail spool file contains characters like this: '\0' . I have a user one of whose messages had such characters. mail -f $MAIL just coredumps. I understand that a message with '\0's in it is a corrupt message, however, the /bin/mail in RedHat 5.x dealt with this fine and about any other mail readers that I have tried either ignore or strip off those characters.
See bug 8100. This has a fix for at least one case where there is a binary zero in the mail text. I didn't notice this bug (6859) when I submitted the report for 8100. Sorry!
*** This bug has been marked as a duplicate of 8100 ***