I have a project where I use Hudson TextFinder to scan the console log for build errors.
If the TextFinder finds any errors in the console log the build is failed.
But there is no mail sent to upstream committers.

If the builds fail in a "normal way" the mails are sent correctly.

TextFinder is setup to search for FAILURE:*

console.log
Archiving artifacts
Recording fingerprints
Checking console output
/home/<user>/.hudson/jobs/<job>/builds/2010-04-21_10-58-04/log:
FAILURE: could not ...
Finished: FAILURE

(I could not find the blame upstream committers plugin in the component list.)