KDE kmail before 5.5.2 and messagelib before 5.5.2, as distributed in KDE Applications before 17.04.2, do not ensure that a plugin's sign/encrypt action occurs during use of the Send Later feature, which allows remote attackers to obtain sensitive information by sniffing the network.
https://commits.kde.org/messagelib/c54706e990bbd6498e7b1597ec7900bc809e8197
https://commits.kde.org/kmail/78c5552be2f00a4ac25bd77ca39386522fca70a8