PowerShell Commands to Extract External User Email Addresses

Question

There is a need to retrieve email address information of external users for supporting an email campaign. Looking for PowerShell commands that can extract all email addresses from the mailbox, specifically targeting external users outside the organization.

Additionally, the goal is to perform this action for all users in the organization simultaneously.

Note: Emails from the past 4-5 years are visible in the Outlook account, but verifying every email manually is a big process. Any assistance or possibilities to retrieve this data would be appreciated.