At SendGrid, email security is at the core of our business.
Recent revelations about dragnet nation state surveillance have raised awareness about email security to new levels.
With that in mind we are ensuring that ALL email sent via SendGrid will utilize opportunistic encryption using TLS.
Those 8 million domains presented 3.4 million unique mail exchangers, 2,614,380 (76.1%) of which claimed to support TLS. We attempted to connect to all of them, and failed to successfully negotiate a trusted TLS connection with 223,800 of them (8.5%)