Interoffice mail should be limited to items that cannot be scanned and emailed (or posted to a shared folder or workspace). If employees have access to a high speed scanner, no document is too long to be scanned and emailed.
Along with immediate savings on physical delivery costs, scanning more documents will also save money in the long-term. Electronic records are easier to track, store, and retrieve. They take up much less space, etc.
Many agencies/offices understand these benefits, but some will scan a document for electronic recordkeeping *after* processing/circulating the hard copy. Any document that will be scanned eventually, should be scanned immediately (upon receipt) and processed electronically from start to finish.