@JRD: Default FROM is your username@hostname. I can remember that several years ago that was quite easy to forge any FROM with sendmail but now I don`t know how to do it. In fact I never needed it. I`m using this solution only for automation of sending machine-generated PDF reports to people who at home (at night for example) but they need to track these reports somehow. The simplest method to forge FROM would be to define your /etc/HOSTNAME I guess.
@Gapan: Does email allow to send an attachment?
@thenktor: This might be possible, however e-mail provider for our company (we use external mail accounts) doesn`t block this e-mails.