The thunderbird email client plugin enigmail using gnupg2 doesn't work under KDE in Mageia 4. It didn't work in Mageia 3 either. This appears to be due to the addition of gnome-keyring, which seems to block pinentry from asking the user for their passphrase in order to sign/encrypt email, so attempts to send email from thunderbird using enigmail / gnupg2 fail.
The options to work around this are all less than attractive. Uninstalling gnome-keyring doesn't resolve the problem, but it orphans 21 packages. Disabling the enigmail extension in thunderbird re-enables sending email again, but of course then they can't be signed. Uninstalling gnupg2 leaving only gnupg installed with enigmail enabled in thunderbird allows signing of sent email, but that removed a lot of KDE applications and orphaned 169 packages in Mageia 3.
With gnupg2 installed and enigmail enabled in thunderbird and OpenPGP preferences set to find gpg as /usr/bin/gpg2 all the pieces appear to be in place. KDE starts the gpg-agent daemon and sets variable GPG_AGENT_INFO to point to its socket. The user file ~/.gnupg/gpg-agent-info also points to the socket. The user file ~/.gnupg/gpg.conf contains the directive use-agent and specifies the default-key. File ~/.gnupg/gpg-agent.conf contains "pinentry-program /usr/bin/pinentry-qt" and /usr/bin/pinentry-qt is simply a link to /usr/bin/pinentry-qt4 as you'd expect under KDE, while /usr/bin/pinentry doesn't work either.
An OpenPGP debugging log created with all of this set up shows that trying to send an email from thunderbird results in either enigmail or gnupg2 failing with the error "no pinentry". Clearing the OpenPGP preferences entry /usr/bin/gpg2 triggers a warning that gpg-agent can't control passphrase retention because gnome-keyring or another similar service is installed.
This system was upgraded from Mageia 3 to Mageia 4, so I wonder, does this all work in a fresh install of Mageia 4? It looks like this is the result of a conflict between enigmail with gnupg2 and gnome-keyring, but if anyone has made this work I'll appreciate hearing about it. I'd like to be able to sign/encrypt email, but I'd also like to have a full KDE desktop.