As reported by The Verge, Twitter started sending emails to the holders of accounts who had not signed in for six months or more:

The field of Brand Protection has historically been relegated to those companies who produce products that are subject to counterfeit production. This includes popular consumer products and luxury goods.

However, the rise of social media popularity in business has fostered a counterfeit culture for accounts. In recent years, a growing number of businesses have wisely allocated resources towards social media brand protection, but the vast majority of businesses still have gaping vulnerabilities in their social media governance approach. If exposed, these vulnerabilities would inflict substantial reputation damage.