If you are using the email-ext Jenkins plugin to send out emails, there is a "build" object that contains a lot of information about your Jenkins job.

I would do the following:

1. Print out the properties inside this object by adding the following code to your template:

   <% println build.properties.collect{it}.join('<br />') %>

2. View the email template output. You can either use the Jenkins "Email Template Testing" feature or just run your job. You should see a whole bunch of "KEY=VALUE" print outs.

3. Look for the environment variable you are interested in. If your environment variable is listed in environment={BUILD_NUMBER=45, BUILD_DISPLAY_NAME=#45...}

   , you can just call build.environment['BUILD_NUMBER'] to get 45.

4. If you want to inject custom environment variables I would suggest installing the Env Inject Plugin, defining your variables through that plugin and then looking for the variable in build.envVars