Contacts and calendars are working with Outlook 2016 and Nine on Android! 
Sending mails works but the mails in the folders are not shown. As a workaround one may setup a separate IMAP account.
/etc/httpd/conf.d/horde.conf:
Alias /Microsoft-Server-ActiveSync /usr/share/horde/rpc.php
Alias /autodiscover/autodiscover.xml /usr/share/horde/rpc.php
Alias /Autodiscover/Autodiscover.xml /usr/share/horde/rpc.php
Alias /AutoDiscover/AutoDiscover.xml /usr/share/horde/rpc.php
RewriteEngine On
#RewriteRule ^/Microsoft-Server-ActiveSync /usr/share/horde/rpc.php [PT,L,QSA]
RewriteRule .* - [E=HTTP_MS_ASPROTOCOLVERSION:%{HTTP:Ms-Asprotocolversion}]
RewriteRule .* - [E=HTTP_X_MS_POLICYKEY:%{HTTP:X-Ms-Policykey}]
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
ActiveSync settings:
$conf['activesync']['params']['driverconfig'] = 'horde';
$conf['activesync']['storage'] = 'Sql';
$conf['activesync']['emailsync'] = true;
$conf['activesync']['version'] = '14.1';
$conf['activesync']['auth']['type'] = 'basic';
$conf['activesync']['autodiscovery'] = 'user';
$conf['activesync']['outlookdiscovery'] = false;
$conf['activesync']['logging']['path'] = '/var/log/horde/activesync.log';
$conf['activesync']['logging']['type'] = 'onefile';
$conf['activesync']['ping']['heartbeatmin'] = 60;
$conf['activesync']['ping']['heartbeatmax'] = 2700;
$conf['activesync']['ping']['heartbeatdefault'] = 480;
$conf['activesync']['ping']['deviceping'] = true;
$conf['activesync']['ping']['waitinterval'] = 15;
$conf['activesync']['enabled'] = true;
I get an error in /var/log/horde/activesync.log when syncing mails, I tried playing with horde permissions but no success:
[53228][2018-06-28T22:50:56+00:00] >>>: Polling Horde_Core_ActiveSync_Driver::_getMailFolders()
[53228][2018-06-28T22:50:56+00:00] ERR: User markus is not authorized for Mail