This is nothing new, but lots of organizations have miserable processes to unsubscribe.
The law and best practices say mass emails need to have a link that allows people to opt themselves off of an email list.
One way to not do this is to link email and customer status that you have to stop being a customer to stop getting emails:
I don't care if you work hard to make your emails relevant to your customers, Washington Green Grocer. I should be able to pay you for overpriced produce deliveries without getting spam.