> Is any of that server-to-server journey ever encrypted? It can be, thanks to RFC 3207 (STARTTLS). However, unless you configure your sending MTA to require

> Is any of that server-to-server journey ever encrypted? It can be, thanks to RFC 3207 (STARTTLS). However, unless you configure your sending MTA to require TLS (and in turn give up the ability to send email to a large swath of the internet) you have no protection against a MITM adversary hiding the recipient's advertisement of STARTTLS.