Probably because mail_open() in libc/mail.c tries to unlink something after freeing it: (unidiff format) --- 1.1 1993/02/24 18:34:16 +++ mail.c 1993/02/24 19:59:07 @@ -217,8 +217,8 @@ errno = eno; return NULL; } - mail_free(scratch); (void) unlink(scratch); + mail_free(scratch); /* Housekeeping */