To send .xlsx file as email attachment

Hi,

I need to send .xlsx file as an email attachment.

Currently using   SO_DOCUMENT_SEND_API1, however this does not allow length 4 extensions.

Tried using a Z structure having doc_type field of length 4..but not working.

Also tried using cl_document_bcs=>add-attachment..but this too refers to a structure SOODK having objtype field of length 3.

Pl suggest.

Thanks.