From ${URL} : In KDE KMail 5.10.3, an attacker in possession of S/MIME or PGP encrypted emails can wrap them as sub-parts within a crafted multipart email. The encrypted part(s) can further be hidden using HTML/CSS or ASCII newline characters. This modified multipart email can be re-sent by the attacker to the intended receiver. If the receiver replies to this (benign looking) email, they unknowingly leak the plaintext of the encrypted message part(s) back to the attacker. Reference: https://bugs.kde.org/show_bug.cgi?id=404698 @maintainer(s): after the bump, in case we need to stabilize the package, please let us know if it is ready for the stabilization or not.
19.04.3 was stabilised, cleanup done in 420336464e757748fd3f7b63bdb565f3529b203c
KDE team is done here, anyway.