Make sure OCR (Searchable) is off, it massively increases file size if there is cursive anywhere in the document.
If they need OCR, they will have to retrieve the big PDF and use something else to make it smaller.
I have a client that is having periodic scanning issues. They scan to a Network Folder, Black & White, 300x300 dpi. They randomly have issues where the file size will be huge. Scanning a document that is 70 pages and it is a 36,900KB PDF. Then they will scan a 400 page document, without changing any settings, and the document will be like 11,000KB. The issue the occurs is the file size is to large to send through email. Is there something that I can change to get them to stop having periodic issues. For the most part they dont have any issues, just sometimes they get a huge PDF.