What are other companies doing for their workers who don't have work email addresses?

Our client has a large employee population that never get provisioned a work email address when they start with the company based on their company email policy. Because of this, there is no way for them to receive email notifications for any system notifications unless we populate their work email address with an email they have access to. We don't want to populate this with their personal email address due to concerns with them receiving confidential information (i.e. salary or PII changes) to a yahoo or hotmail account.

Curious what other implementation partners have done for similar companies that may not provision work email addresses for their population.