Donors have always been able to control when and where they receive emails from their donor account. Now, they can disable donation receipt emails in one click (or tap) right from the email itself.
Once clicked, Adam (who leaves donating up to Theresa and doesn't particularly want donation receipts) would see a confirmation message.
From the recent Joint Donor feature announcement,
"When two donors are joined, their donations will be combined into a single donation history. When one donor gives, it's as if both donors gave. Each will get a receipt in accordance with their personal communication preferences."
Some donors like this change as it recognizes that they, a joint donor, gave a donation! Others don't like it because they don't particularly want these email receipts and they never signed up for them.
Although we think sending donation receipts to joint donors is the right thing to do, we wanted to make it easier for those who don't like getting donation receipts to disable them.