How to send an email with image files and the the images are shown on page instead of being attachments ?

Your email must satisfy the following rules:

1. it’s a multi-part email

2. it has an "html" as one of its parts (content type must be set)

3. every image must have a header like "Content-ID: <some-id>", and of course, content type must be set

4. the <img> tags in your html must use "cid" to refer to these images, such as "<img src=’cid: some-id’/>