I write an application to create a draft message with an attachement

when i call soap for SaveDraftRequest it work fine
but i can't send the Multipart Centent with base64 encoding

I found "Content-type" and "Cont-disp"

But how in soap attirbute of MP add the "Content-transfer-encoding: base64" directive ?

How can i add "Content-transfer-encoding" for the MP content

Or must i upload the attachement before or after adding draft

That a part of the request :

<SaveDraftRequest xmlns="urn:zimbraMail">
<mp ct="multipart/mixed">
<mp body="1" ct="text/plain" part="1"><content>Hello</content></mp>
<mp cd="attachment;filename=&quot;MAILCIE.text&quot;"
ct="application/octet-stream;name=&quot;MAILCIE.text&quot;" part="2.1.1">
<content>PGh0bWw+CiAgPGhlYWQ+CiAgPC9oZWFkPgogIDxib 2R5PgogICAgPHA+VGhpcyBpcyB0aGUgYm9keSBvZiB0aGUgbWV zc2FnZS48L3A+CiAgPC9ib2R5Pgo8L2h0bWw+Cg==</content>