This is somewhat true. RFC3207[1] describes opportunistic TLS encryption for SMTP communications. Our postfix deployment uses this and a fair amount of our email is sent over TLS-encrypted SMTP.
Of course, an MITM attack could hide the STARTTLS option and there are questions around the strength of the CA cert infrastructure, but SMTP is not just plaintext.
Of course, an MITM attack could hide the STARTTLS option and there are questions around the strength of the CA cert infrastructure, but SMTP is not just plaintext.
[1] https://tools.ietf.org/html/rfc3207