Send Message with DocumentReference

Hi,
I work with API. I create a new Mail, attach DocumentReference for the Mail.
Then I send the Mail. A size of the draft and send Mail is very small.
Size does not depend on the size of attached document.
The contents of the document can not be attached in the Mail.
When I send a mail by client Groupwise its size depend on the size of attached document.
What is the reason?

When I try to open a letter in Novell WebAccess,
the programm generates an error "Unable to read attachment",
but I can open and view a attachment in Client Groupwise.

Please help me

Thank you