This type of STARTTLS stripping attack has mostly gone unnoticed because it tends to be applied to residential networks, where it is uncommon to run an email server2. STARTTLS was also relatively uncommon until late 2013, when EFF started rating companies on whether they used it. Since then, many of the biggest email providers implemented STARTTLS to protect their customers. We continue to strongly encourage all providers to implement STARTTLS for both outbound and inbound email. Google's Safer email transparency report and starttls.info are good resources for checking whether a particular provider does.