Almost all commercial mails, including newsletters, past orders, discount offers based on purchases, etc., use an "unmonitored mailbox" or an invalid address to send information. Any reply, manual or automatic, will never get seen by anyone on the other side to take any sort of action.
The only way out is to trawl through one's account, hoping that at least one mail from each contact is available, and then changing the email address with each of those. For personal contacts, this would involve emailing them and hoping they see it. For commercial contacts, it would involve going to the respective site and figuring out how to change the address and confirm the new address. Overall, this would be a cumbersome process for many people.
The only way out is to trawl through one's account, hoping that at least one mail from each contact is available, and then changing the email address with each of those. For personal contacts, this would involve emailing them and hoping they see it. For commercial contacts, it would involve going to the respective site and figuring out how to change the address and confirm the new address. Overall, this would be a cumbersome process for many people.