SharePoint mail handler could not extract attachment from a certain type of eml emails

Question

I found out why SharePoint mail handler could not extract attachment from a certain type of eml emails. The eml emails not working me were constructed with this structure, using one attachment as example:
If I removed the highlighted red part, it just worked.
----boundary_2_6a659de7-74df-40e1-ab98-225ccc22717a
Content-Type: multipart/alternative;
boundary=--boundary_1_9786ce6d-49bd-4ef9-9300-4ed4797bd8ad
----boundary_1_9786ce6d-49bd-4ef9-9300-4ed4797bd8ad
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: base64
{body
text/plain in base64 string}
----boundary_1_9786ce6d-49bd-4ef9-9300-4ed4797bd8ad
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: base64
{body
text/html in base64 string}
----boundary_1_9786ce6d-49bd-4ef9-9300-4ed4797bd8ad--
----boundary_2_6a659de7-74df-40e1-ab98-225ccc22717a
Content-Type: multipart/mixed; boundary=--boundary_3_e5f4edb0-f72c-44d3-9cea-f01b51affe53
----boundary_3_e5f4edb0-f72c-44d3-9cea-f01b51affe53
Content-Type: application/octet-stream;
name=attachment.pdf
Content-Transfer-Encoding: base64
{attachment
in base64 string here}
----boundary_3_e5f4edb0-f72c-44d3-9cea-f01b51affe53
----boundary_2_6a659de7-74df-40e1-ab98-225ccc22717a--
I know little about eml file structure. Either the structure is wrong or the sharepoint has a bug!

Answer 1

Also, here's the list of classes imported in my java code:
import oracle.apps.xdo.delivery.DeliveryManager;
import oracle.apps.xdo.delivery.DeliveryRequest;
import oracle.apps.xdo.delivery.DeliveryPropertyDefinitions;
import oracle.apps.fnd.common.AppsContext;
Not sure where to refer the "Attachment" class. Thanks.