XI message with Attachment using Http Adapter

Hi ,

We are using XI/PI 7.0 with Sp09 and Sender Application is SRM and Receiver is Ariba MarketPlace.

We are trying to Send PO with Attachments like Word, PDF etc from SRM to Ariba using Https adapter and from SRM we are using ABAP Proxy. When I did the testing with out any special config, I was able to send the attachments (I can see word doc as part of the payload-attachment) to XI from SRM but this attachment is not going through https adapter from XI to Ariba?

I have read some posts on this but I could not find the answer for my situation. One of the solution is that we can use SOAP adapter but we don't want to use Soap for some reasons.

Please give your thoughts.

Thanks in Advance.

-Laxman