evolution-data-server (eds) through 3.36.3 has a STARTTLS buffering issue that affects SMTP and POP3. When a server sends a "begin TLS" response, eds reads additional data and evaluates it in a TLS context, aka "response injection."
https://www.debian.org/security/2020/dsa-4725
https://usn.ubuntu.com/4429-1/
https://security-tracker.debian.org/tracker/DSA-4725-1
https://security-tracker.debian.org/tracker/DLA-2281-1
https://lists.debian.org/debian-lts-announce/2020/07/msg00012.html
https://gitlab.gnome.org/GNOME/evolution-data-server/-/issues/226