If you can send that volume, the main value is offering sending services to others. Many marketers need reliable infrastructure for newsletters, promotions, or product launches.
You could partner with affiliate marketers, agencies, or SaaS companies that run large campaigns. They often need high volume sending capacity.
Another option is offering bulk email delivery as a service. Clients provide the list and content, and you handle the sending.
Just make sure everything is permission-based. Sending to scraped or random lists will quickly damage the servers and get them blacklisted.