Exposure of Sensitive Information to an Unauthorized Actor in Jenkins-mailer-plugin

jenkins-mailer-plugin before version 1.20 is vulnerable to an information disclosure while using the feature to send emails to a dynamically created list of users based on the changelogs. This could in some cases result in emails being sent to people who have no user account in Jenkins, and in rare cases even people who were not involved in whatever project was being built, due to some mapping based on the local-part of email addresses.