UTL_MAIL, no Date attribute

I have tested telnet and the UTL_SMTP package on my database server for sending email. In each I have verifiied that if I include 'Date:' in the sent DATA attribute, that I receive the email with a Sent date in the email header. However with the UTL_MAIL package, it does not appear to have the ability to send a Date into the email header. I tested the package and successfully received mail. We use an email shareware product here rather than something like Outlook. Have I missed something or can someone explain why a Date attribute is not defined in the