The default Jenkins email notifications are almost unusable, they contain a complete output of the build log. How to set up custom notifications:

Install this plugin: https://wiki.jenkins-ci.org/display/JENKINS/Email-ext+plugin
Configure a Jenkins job, scroll to the bottom and click "Add post-build action", then select "Editable email notification"
Example email design:

Subject: [CI] Nightly "master" test results - Build #${BUILD_NUMBER} - ${BUILD_STATUS}

Body:

Nightly master tests

Test run #${BUILD_NUMBER} for "${PROJECT_DISPLAY_NAME}"

Summary

Result: ${BUILD_STATUS} - ${TEST_COUNTS, var="fail"} failures

${TEST_COUNTS, var="pass"} out of ${TEST_COUNTS, var="total"} tests passed (${TEST_COUNTS, var="skip"} skipped).

${FAILED_TESTS, showStack=false, showMessage=false}