Was trying out the KDE Plasma desktop on Fedora and after closing Geary, it periodically launches by itself without user intervention, with a prompt to login to one of the listed e-mail accounts as it could not otherwise connect to the mail server specified.
This is the first I've seen this behavior from Geary, but it has not (so far) occurred with any other desktop I have installed (MATE, LXDE, LXQt).
