You may overfrank or underfrank your mail, and therefore overpay or underpay for your mailings, and potentially delay your business critical mail. If you underfrank your mail you could be liable to surcharges, plus the difference per item. It is also the customer’s responsibility to have an up to date tariff installed in their franking equipment. Failure to use the correct tariff may render the franking equipment inoperable. Further information from Royal Mail Scheme for franking letters and parcels 2015.