Cost distribution when using Amazon S3

Hi.
Some months ago we configured S3 as volume for Powerstore. We have ~27G of data stored there, but we get relatively high invoices from Amazon. I.e. last one was 10.54$, 1.98$ for storage and 8.56$ for bandwidth! In one month we have 95GB of data being transferred out.

We store in S3 mails older than 3 years, so unlikely we can produce nearly four times the data in transfer.

Why that? Backup?

Thanks