When we use the plugin email-exit , we can give any email id in the 'from' field and it will send an email from the ID which is specified in the 'from' field.

Example pipeline:

pipeline {
    agent any
    stages {
        stage('test') {
            steps

{                 // Your build steps here                 echo 'Building...'                 // Send email notification using emailext plugin within the build stage                 emailext mimeType: 'text/html',                          body: 'Test Message',                           subject: 'test sub',                          from: 'noorjahan.s@allianz.com',                          to: 'noorus1218@gmail.com'             }

        }
    }
}

Here, the mail will come from noorjahan.s@allianz.com. If I change the from mail id to somebody else, say renjith@allianz.com then a mail from renjith@allianz.com is received. And the mail is not visible in the sent items of the sender. So in this way, anybody can change the from mail id and send emails from others' email id by impersonating them.