DATA: message  TYPE REF TO cl_bcs,      " envelope
      document TYPE REF TO cl_document_bcs,   " letter
      .
DATA body_text TYPE soli_tab.
DATA subject_line TYPE so_obj_des VALUE 'asdasdasd'.
DATA size TYPE sood-objlen.
DATA xmlstr     TYPE xstring.
DATA lt_bintab  TYPE solix_tab.


message  = cl_bcs=>create_persistent( ).  " message = the email itself
APPEND 'Hello World!' TO body_text.     " body_text is an internal table
* think of message as the envelope, and document as the letter.
document = cl_document_bcs=>create_document(
  i_type = 'RAW'
  i_text = body_text                    " again, this is just a table containing your message body
  i_subject = subject_line ).           " subject_line is just text, too

lt_bintab = cl_bcs_convert=>xstring_to_solix( iv_xstring = xmlstr ).

* now you are going to attach your spreadsheet to the letter
size = lines( lt_bintab ).
size = size * 255.
document->add_attachment(
i_attachment_type    = 'XLS'
i_attachment_subject = 'filename'     " your file name
i_attachment_size    = size                         " output of the string_to_solix method
i_att_content_hex    = lt_bintab ).