I'll give you the benefit of the doubt that this is a real question-- the postal system is designed to allow companies to send letters to customers. Using the postal system in the way it was intended is the opposite of abuse.
If you want to change some process, you'll want to make a business case. The first question to ask is what benefit the company derives (or expects to derive) from the current process. Are these letters advertising? Reminders? Something else? Then determine an alternative that produces the same benefit for a lower cost and make a case for this alternative. I, for example, am quite happy that my broker lets me opt in to receiving my annual mutual fund prospectuses electronically rather than getting hundreds of pages of paper mailed to me every year that get discarded almost immediately. Perhaps you could suggest building a system that allowed customers to opt to receive some or all of this mail electronically for example.