How to obtain a list of email aliases

/**

 * list users that have email aliases

 * Usage:

 * 1. copy and paste this source code to your Apps Script Editor

 * 2. select the following function name

 * 3. click 'Run'.

 * 4. The users with email aliases will be printed in the 'Execution log'

 *

 * © 2021 xFanatical, Inc.

 * @license MIT

 * @version 1.0.2 fix a pagination issue

 * @version 1.0.1 print out aliases

 * @version 1.0.0 proof of concept

 */

function listUsersWithEmailAliases() {

  let pageToken

  let page

  do {

    page = AdminDirectory.Users.list({

      customer: 'my_customer',

      maxResults: 100,

      pageToken,

      fields: 'users(name/fullName,primaryEmail,aliases),nextPageToken',

    })

    let users = page.users

    if (users) {

      for (let i = 0; i < users.length; i++) {

        const user = users[i]

        if (user.aliases && user.aliases.length > 0) {

          Logger.log(`User ${user.name.fullName} <${user.primaryEmail}> `

            + `has ${user.aliases.length} email alias${user.aliases.length > 1 ? 'es' : ''}: `

            + JSON.stringify(user.aliases))

        }

      }

    } else {

      Logger.log('No users found.')

    }

    pageToken = page.nextPageToken

  } while (pageToken)

}