Two problems I can see:
1. You have not defined what "does not seem to work" means. You get no
log output in your emails? You get unexpected output? Jenkins shows an
error message when sending the email? etc...
2. Your example code misspells "BUILD_LOG_EXCERPT".
As you're apparently using an old version of email-ext, and a modified
(SNAPSHOT) version of Jenkins, you could also try upgrading, and using
an official Jenkins release.
-Chris