Amazon servers reject TLS connections in certain cases, for example when third party sellers on Amazon communicate with customers vie email. This means that millions of emails that are sent via Amazon may be exposed everyday.
Violation of GDPR. Article 32 of the GDPR requires companies to implement “appropriate” security measures, such as encryption, to protect the confidentiality of communications. As TLS encryption is very cheap and simple to implement and the number of sellers and customers on Amazon is very high, it seems inappropriate to neither require not allow TLS for emails.
Source: Complaint: Amazon doesn’t allow baseline TLS security