Possibly depending on your mail server and network monitoring. There could be clues in the mail server or print logs. If your mail server keeps a copy of all mail sent through it and you are a manager then it might be possible to ask HR for permission to review one of the recipients email accounts who received the confidential email if you suspect a problem. Keep in mind there are plenty of ways to get around that tracking such as copy & pasting an email into a 3rd party email service, using a different smtp server for sending email, or taking a picture of the email with their phone.