Horde and activesync works on a raspberry in a first test with Outlook as client!
Enable unofficial epel repo and install horde:
mv /etc/yum.repos.d/epel.repo ~
cat > /etc/yum.repos.d/epel.repo << EOF
[epel]
name=Epel rebuild for armhfp
baseurl=https://armv7.dev.centos.org/repodir/epel-pass-1/
enabled=1
gpgcheck=0
EOF
yum clean all
yum install https://nethserver.globalcortex.net/mirror/devtest/nethserver-horde-0.0.1-1.16.gd07f9c5.ns7.noarch.rpm
Enable activesync (which installs the activesync module via pear as it’s not in the unofficial epel repo - thanks @m.traeumner):
config setprop horde activesync enabled
signal-event nethserver-horde-update
You have to enable Activesync in the Horde web UI too. Don’t test on a production system!