Unfortunately I don't see anything suspicious in the logs. (ie no exceptions, no errors, no info) related to this.
This leads me to believe it's "working", but not in the way I would expect it to.
I'm also going to try free-style project, to see if it's just something weird with maven projects.

Can you view the source of the email? I'm wondering if the content is there, but there are < > in the content which is causing it to be read as HTML. This would explain also why the content you have after is not showing up.

I looked at the raw source of the email and the content is not there.
Also, I did a free style build (instead of a maven build), and the entire contents of the log gets displayed in the body of the email.
In other words, this works for free style projects: ${BUILD_LOG, maxLines=9999, escapeHtml=false}
But not for maven builds.

Hope this helps.

Hmmm, I have very little experience with Maven projects, so I don't know how they are different if at all. Do you know the class of the Maven project, I can look if it does log stuff differently.

No problem! When I get to work tomorrow I'll create some detailed steps to reproduce this problem.
One other piece to the puzzle is that I'm using Cloudbees Jenkins, which means that the slaves are dynamically provisioned to run a build.
I don't know if that bit of information is useful or not, but I thought I'd let you know.

I added a dummy pom.xml to this jar. In Jenkins create a new "Maven project" (I attached a screenshot of creating this type of project). I don't know if you need a plugin to create a Maven project, or if it comes out-of-the-box-Jenkins.

In the configuration of the job, point it to the pom.xml and select "test" as the target (I've attached a screenshot of this too).

The build will fail, since there are no sources, but it doesn't have to pass to reproduce this problem.

When you build it, the text on the console will have something like:
==========================
blah blah blah
blah <===[JENKINS REMOTING CAPACITY]===>
blah blah blah
Failure
==========================
The message body will only contain stuff above the "Jenkins Remoting Capacity" text.

On a side note, I'm also going to try to get rid of one other variable: Cloudbees. I'm going to install Jenkins locally on my machine and try to reproduce this. I'm more and more convinced that it has to do with how Jenkins Cloudbees handles the console text. The reason I say this is because if I just try to echo out the contents of the console text, it works fine.

I will let you know my results.

I am getting the following:

Started by user anonymous
Building in workspace /home/user/Projects/email-ext-plugin/work/workspace/JENKINS-17838
No emails were triggered.
Parsing POMs
JENKINS-17838 $ java -Xdebug -Xrunjdwp:transport=dt_socket,server=n,address=47661 -cp /home/user/Projects/email-ext-plugin/./work/plugins/maven-plugin/WEB-INF/lib/maven3-agent-1.2.jar:/home/user/bin/apache-maven-3.0.5/boot/plexus-classworlds-2.4.jar org.jvnet.hudson.maven3.agent.Maven3Main /home/user/bin/apache-maven-3.0.5 /home/user/Projects/email-ext-plugin/target/work/webapp/WEB-INF/lib/remoting-2.23.jar /home/user/Projects/email-ext-plugin/./work/plugins/maven-plugin/WEB-INF/lib/maven3-interceptor-1.2.jar 40854
ERROR: transport error 202: connect failed: Connection refused
ERROR: JDWP Transport dt_socket failed to initialize, TRANSPORT_INIT(510)
JDWP exit error AGENT_ERROR_TRANSPORT_INIT(197): No transports initialized [../../../src/share/back/debugInit.c:741]
FATAL ERROR in native method: JDWP No transports initialized, jvmtiError=AGENT_ERROR_TRANSPORT_INIT(197)

Not sure what the issue is...

Weird. I just tried this on a clean windows machine. I installed Jenkins, created a dummy maven job, and pointed it to the pom that I attached. I didn't even indicate a maven target.
The only thing I can suggest is to make sure that under Manage Jenkins, you specify a Maven Install (I attached a screenshot called mavenInstallation.png which shows a screenshot of my maven configuration.)

I just tried this again, it looks like because I am running under the Netbeans debugger it causes an issue with running the Maven. When I just run (without the debugger) I am still not able to reproduce this issue with the Maven job. I get the following output in the email that is sent to me.

Started by user anonymous
Building in workspace /home/USER/Projects/email-ext-plugin/work/workspace/JENKINS-17838
No emails were triggered.
Parsing POMs
[JENKINS-17838] $ java -cp /home/USER/Projects/email-ext-plugin/./work/plugins/maven-plugin/WEB-INF/lib/maven3-agent-1.2.jar:/home/USER/Projects/email-ext-plugin/work/tools/hudson.tasks.Maven_MavenInstallation/Default/boot/plexus-classworlds-2.4.jar org.jvnet.hudson.maven3.agent.Maven3Main /home/USER/Projects/email-ext-plugin/work/tools/hudson.tasks.Maven_MavenInstallation/Default /home/USER/Projects/email-ext-plugin/target/work/webapp/WEB-INF/lib/remoting-2.23.jar /home/USER/Projects/email-ext-plugin/./work/plugins/maven-plugin/WEB-INF/lib/maven3-interceptor-1.2.jar 47250
<===[JENKINS REMOTING CAPACITY]===>   channel started
log4j:WARN No appenders could be found for logger (org.apache.commons.beanutils.converters.BooleanConverter).
log4j:WARN Please initialize the log4j system properly.
Executing Maven:  -B -f /home/USER/Projects/email-ext-plugin/work/workspace/JENKINS-17838/pom.xml test
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building foo 1.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.5:resources (default-resources) @ foo ---
[debug] execute contextualize
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/USER/Projects/email-ext-plugin/work/workspace/JENKINS-17838/src/main/resources
[INFO]
[INFO] --- maven-compiler-plugin:2.3.2:compile (default-compile) @ foo ---
[INFO] No sources to compile
[INFO] [debug] execute contextualize
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/USER/Projects/email-ext-plugin/work/workspace/JENKINS-17838/src/test/resources

[INFO] --- maven-resources-plugin:2.5:testResources (default-testResources) @ foo ---
[INFO] [INFO] No sources to compile

[INFO] --- maven-compiler-plugin:2.3.2:testCompile (default-testCompile) @ foo ---
[INFO]
[INFO] --- maven-surefire-plugin:2.10:test (default-test) @ foo ---
[INFO] No tests to run.
[INFO] Surefire report directory: /home/USER/Projects/email-ext-plugin/work/workspace/JENKINS-17838/target/surefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------

Results :

Tests run: 0, Failures: 0, Errors: 0, Skipped: 0

[JENKINS] Recording test results
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 7.681s
[INFO] Finished at: Wed May 15 04:37:41 MST 2013
[INFO] Final Memory: 8M/59M
[INFO] ------------------------------------------------------------------------
[JENKINS] Archiving /home/USER/Projects/email-ext-plugin/work/workspace/JENKINS-17838/pom.xml to /home/USER/Projects/email-ext-plugin/work/jobs/JENKINS-17838/modules/foo$foo/builds/2013-05-15_04-37-27/archive/foo/foo/1.0/foo-1.0.pom
Waiting for Jenkins to finish collecting data
channel stopped
Email was triggered for: Success
Sending email for trigger: Success

All done success!

OK. It looks like you've done your due diligence on this, and if you're OK we can probably close this out. The workaround of attaching the log is more than acceptable. I noticed that Cloudbees is not using the latest and greatest version of the mail-ext plugin (2.2.8, not 2.2.9), so there may be other issues going on. Thank you so much for looking into this. I'll continue trying out some things and if I make any progress I'll update this Jira. Thanks!