Add an attachment to the message.
Parameters: id - unique identifier for the attachment Parameters: content - attachment content throws: MessagingException - failed to add attachment
Retrieve attachment with the specified identifier.
Parameters: id - unique identifier for attachment DataHandler representing attachment content, or null if anattachment with the specified identifier is not found
Removes attachment with the specified unique identifier.
Parameters: id - attachment identifier throws: MessagingException - failed to remove attachment