The remote host may be tricked into running an executable file
The remote host is running a version of the Eudora mail client that doesn't properly warn when a user attempts to view an executable attachment. Specifically it doesn't give out warning messages if a user attempts to open a file that doesn't have one of the following extensions: .exe, .com, .bat. So, for example, an attacker can bypass the warnings by using a .lnk file to launch an executable.
Edit the Eudora.ini file and add lnk to the WarnLaunchExtensions list or upgrade to the latest version