Sure, but a user has no way of knowing if their mail client does opportunistic STARTTLS or not. It's not something the average user can test, and not something

Sure, but a user has no way of knowing if their mail client does opportunistic STARTTLS or not. It's not something the average user can test, and not something mail clients would typically feel the need to mention. On the other hand, you can tell people that good practice is to use ports 993 for IMAP and 465 for SMTP and they'll be good to go, that using any other ports opens them to potential attack.