+1, We noticed to issues while using the two plugins, for us:
Jenkins: 1.446
Config slicing plugin: 1.28.1
Email-ext plugin: 2.16

First issue was that the Slicer only was modifying the default setting (which we do not use, we use the Failure case almost always.)
Secondly the default subject and default content was not filled out by default. We started to get a ton of e-mails with no subject nor body. After consulting with the team we realized we'd recently made these changes using the slicer and they were not being filled out.

I've added a new ticket to address William's issues
https://issues.jenkins-ci.org/browse/JENKINS-13834

I've extended the Slicer to configure the triggers of the Email-Ext-plugin with version 2.18 or higher.
The attached patch file contains the necessary changes on the code. It would be great, if these changes could find the way into the next release of the Slicer.

Fixed problem with empty email body and subject. An updated patch file is attached.

I tried applying this patch, and in some cases it works, but I noticed I was getting errors like

javax.servlet.ServletException: java.lang.NoSuchMethodError:
hudson.plugins.emailext.plugins.EmailTriggerDescriptor.getTriggerName()Ljava/lang/String;

So, I upgraded the POM to the latest version of the plugin

		<dependency>
			<groupId>org.jenkins-ci.plugins</groupId>
			<artifactId>email-ext</artifactId>
			<version>2.34</version>
			<scope>compile</scope>
			<optional>true</optional>
		</dependency>

And now the patch has compilation errors in over a dozen places. This is a big challenge with the configuration slicing plugin - it is very hard to keep up with changes to the plugins it slices. If the authors of the email-ext plugin want to maintain the slicer, that would be awesome. But I cannot commit the patch as-is.