Have you ever moved and not filed a forwarding address with the Postal Service? Or maybe you keep getting letters for someone who used to live where you are now? Did you ever send a letter with an error in the address?

If you answer 'yes' to any of those, it might make you shrug your shoulders as no big deal, but to the Postal Service it means big money, with figures showing the mail system spent $1.5 billion in 2014 simply due to wrong addresses on letters.

"As many as 40 percent of people who move do not inform the Postal Service," internal investigators reported, which means the Postal Service has to expend energy - and resources - to deal with that undelivered mail.

In a report released Monday, the Postal Service says in 2014, 6.6 billion pieces of mail were identified as "Undeliverable as Addressed" (UAA) - "because the address is illegible, incomplete or incorrect."

"UAA mail is costly," the report found, "since it must be forwarded, returned or treated as waste."

How costly?

In Fiscal Year 2014, "the Postal Service incurred $1.5 billion in costs processing UAA mail," according to a new report from the Inspector General of the Postal Service.

Who is mainly at fault for mail that has the wrong address?

+ 40 percent is "public error" - mainly from people not telling the Postal Service of their new address after a move

+ 35 percent is due to business mailers that have a wrong address

+ 23 percent of the undelivered mail is due to errors made by the Postal Service, like sorting errors or failed deliveries.

Despite efforts to reduce undeliverable mail, that error rate has gone up in recent years from 4.17% of all mail in 2011 to 4.26% in 2014.

What happens to undeliverable mail? The internal report said in 2014, 63 percent was treated as waste (that's over 4 billion pieces of mail), 22 percent was returned to the sender, and another 15 percent was forwarded to the correct address.

Responding to the report, Postal Service officials said new technology is being evaluated to reduce the amount of mail that can't find a home.

All of that takes up money and resources, neither of which is running in the favor of the Postal Service.

In fact, the latest financial review shows the Postal Service lost $1.5 billion in just the first three months of this year.