Disable MovableType’s Send Entry Script

The file ‘mt-send-entry.cgi’ in a default MovableType installation can be used to relay spam. If you’re not using the script to allow your users to “Send this Entry by Email”, you can safely remove the file from your MT install or change the permissions so that the script cannot execute.

However, if you need the functionality Ben Trott has posted a fix, but IMHO, you’d be safer pushing this function client-side using a mailto with some JavaScript

Jacques Distler has some more insight and there’s an active discussion on the MovableType Support Forums