save copy of communication sent to end customer

hello
i think that this is a legitimate request from the client : want to log each message content that was sent to their customer.
let say they send to the customer SMS that alerts him that he has some action to do until some date
then , when you have the log with what you sent the customer can not argue that he wasn't alerted
same goes for promotions - if the client claim a discount you can prove what exactly sent to him.
since this a lot of data to store , the common practice is to save it with expiration date on some storage that our client (not the end customer) has access to it for let say a month
then it is our client responsibility to download it in this period of time, then Adobe remove it
Nir