Instead of having the generic "sign up for emails" form, it would be amazing to give donors the option to select what kind of emails they want to receive: Newsletters, special appeals, monthly ministry updates, etc. And they should be able to unsubscribe from specific email categories as well.
We are a university with several different branches. An undergrad program, an online program, a seminary and a radio station. When someone opts out of any one of our emails, they opt out of all of them. Being able to manage the different email categories for our different groups of people would be amazingly helpful.