When you add an attachment to an e-mail, it's displayed in the Attachment field (under the Subject field in newer versions, at the bottom of the window in older versions) if the message is plain text or HTML. When the message format is Rich Text (RTF) it can be anywhere in the message body.
Whether attachment names are included in printouts of the message depends on the message format as well.
Published June 15, 2004. Last updated on May 16, 2011.