Undeclared identifier 'TidAttachment'

Giganews Newsgroups
Subject: Undeclared identifier 'TidAttachment'
Posted by:  Odin Roll-Hansen (od…@istra.no)
Date: Tue, 19 Jul 2005

I am trying to make a program that can send an email with attachments.
I am using Delphi 5 and Indy 10
When I write this line of code;
TidAttachment.Create(idMessage1.MessageParts, AttachmentFileName);
I get the errormessage 'Undeclared identifier 'TidAttachment'
when compiling
What am I doing wrong?
Yours Odin