Answer
For a text/plain content type, use chr(13) as the linefeed character within the message string — Oracle interprets it as a newline in the resulting email. For example: command_sys.mail('', 'example@email.com', 'Line1'||chr(13)||'Line2');. If the content type is text/html instead, use the <br> HTML tag in the message string in place of chr(13) to produce a line break.