I was replying to a critical business email with quick reply (UI attached). Note that in the "To:" it reads the name of one single individual.

After clicking Send and Archive, however, I saw that the email was addressed to both Mike and everyone on the CC list.

This was unexpected, and mortifying.

Whenever I am composing a Quick Reply, I expect that exactly who I see in the recipient list is exactly who receives the email—no more or no less.