If you're using email-ext plugin for Jenkins and you want to execute a command while your email notification is being processed, you can include into your groovy template something like:
<% def cmd = "cmd /c cd " + build.getWorkspace() + " && svn diff -r HEAD" print cmd.execute().text %>
In this example I'm including the latest svn diff in the email. Don't forget that jenkins truncates the email content if its size is bigger than a certain value...
This type of things can be very handful to make your notifications more informative.