For SMTPS you need proper certificates, I have only the Lets Encrypt ones.
Even though I have configured Postfix and Dovecot for secure SMTP, somehow, I don’t get any incoming emails. I did check my configuration and certifificates. So I presumed, some mail servers only use port 25 to deliver emails to me.
openssl s_client -starttls smtp -connect mybox.org:587 -crlf
All this works well, helo test too.
I may be wrong.