How do I scan large black and white documents, creating the smallest file size possible?

I am attempting to scan a 70 page document and prefer it to be a file small enough to send through regular email.  I am not interested in zipfiles, i am not familiar with them.  I have been scanning and converting to .pdf for years, using the lowest dpi reasonable, but my file sizes are still quite large (compared to other .pdf's that are emailed to me).  I know there is a way, just haven't figured it out.

Ed