Postfix TLS over SMTP - RCPT TO prompts renegotiation then 554 5.5.1 Error: no valid recipients
Solution 1:
Pressing "R" in an s_client session causes openssl to renegotiate. Try entering "rcpt to:" instead of "RCPT TO".
You might also try tools that are more suited to SMTP-specific testing, such as Tony Finch's smtpc or swaks.