The EmailAttachment object is a wrapper that holds the attachment as a byte array (the data field), the file name (the name field), and, if necessary, the attachment identifier which is unique for this message (the optional but useful contentId field).

The attachment identifier may be used to insert images in the message body. For this, a unique contentId (for example, myPic) is specified when creating EmailAttachment. Expression like cid:myPic can be used as a path to insert the attachment in the message body. So, to insert an image you can specify the following HTML element: