attachment_name = os.path.basename(attachment_filename)
        attachment_content_b64 = base64.b64encode(b"Minimal test content").decode('utf-8') # Minimal content

        file_attachment = FileAttachment(
            name=attachment_name,
            content_bytes=attachment_content_b64,
            content_type="text/plain"
        )

        email_msg = Message(
            subject=subject,
            body=ItemBody(
                content=body,
                content_type="Text"
            ),
            to_recipients=[
                Recipient(email_address=EmailAddress(address=recipient_email))
            ],
            from_= Recipient(email_address=EmailAddress(address=SENDER_ID_OR_ADDRESS)),
            attachments = [file_attachment]
        )

        request_body = SendMailPostRequestBody(
             message = email_msg,
             save_to_sent_items = False
        )

        await graph_client.users.by_user_id(SENDER_ID_OR_ADDRESS).send_mail.post(request_body)