Alpine before 2.23 silently proceeds to use an insecure connection after a /tls is sent in certain circumstances involving PREAUTH, which is a less secure behavior than the alternative of closing the connection and letting the user decide what they would like to do.
https://lists.debian.org/debian-lts-announce/2020/06/msg00025.html
http://mailman13.u.washington.edu/pipermail/alpine-info/2020-June/008989.html