In the Email Settings dialog you should see three send methods (MAPI, SMTP and "Send directly"), several SMTP settings (server, user-name, etc.), and the Default Reply Email. I don't know of any problems with MAPI and Outlook Express, although you probably do need to fill in the reply address.
Also, configure any virus scanning software you have installed so that it doesn't add text to outgoing messages. I've seen a couple of virus scanners that corrupt outgoing mails that have attachments.
Just as a simple test, try sending a mail with a Word attachment to the same recipient normally, using Outlook Express. ie. Take Express Scribe out of the equation. You may find that the recipient's mail server is rejecting your mail just because it has the attachment.