Printers in offices leave some hidden prints on any printed paper. That's how many people got caught, including a serial killer who used a library printer. Whe

Printers in offices leave some hidden prints on any printed paper. That's how many people got caught, including a serial killer who used a library printer. Whenever one uses company fax machines, these faxes are recorded: some executive in the valley faxed a company report to some hedge fund, she got busted. All outgoing and incoming mails in the corporate server are stored for some years; that's why large companies use third party for mail services, as these third parties are specialized in auditing, spying, etc. The other way people exfiltrate is using steganography: convert normal files into images, then exfiltrate these images via USB, cloud, etc. Maybe, the easiest way is just take pictures of documents with personal phone. That's why air-gapped environments don't let people with personal phones.