IMAPFilter through 2.6.12 does not validate the hostname in an SSL certificate.
https://lists.debian.org/debian-lts-announce/2019/10/msg00040.html
https://github.com/lefcha/imapfilter/issues/142
https://bugs.debian.org/939702
http://lists.opensuse.org/opensuse-security-announce/2020-06/msg00002.html
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00042.html