How do I know? I work for a state government and talk with people at election commissions is all I'll say. That being said, I'm an anonymous poster on the internet. A simple Google search would reveal numerous news articles about it as far back as February of this year.
It's been done this way for years, but with so many people new to mail-in voting, and suspicions of cheating running high, people are looking at everything with a skeptical eye.
Count me as skeptical, especially in these times.