Since the only thing you can attach to an email is a whole file, you will need to create a new file that has only the pages you want. Simply copy and paste the pages you want into a new document, name it something like "My Script Pages 25-35" (without quotes) and save it.
If you need the correct page numbers in the new document, go to Document > Header and Footer > Options and enter the starting page number (in this example, 25) into the box. Save the file again and attach it to the email.
Final Draft gives you the ability to create a PDF of only the pages you want; you can filter the output by selected pages, page ranges, selected scenes or by a particular revision set. These PDF options are found under File > Print.