[horde] H6 Active Sync authentication error

[horst.simon2 at icloud.com]

Active Sync gives me authentication error, the username (horst at address.net) is the full email address, but when I check the logs it shows only the name from before the @. 
Carddav and Caldav authenticating correct.
Following are the log entries:
2026-04-13T15:34:43+10:00 DEBUG: HORDE [horde] Horde_Rpc::__construct complete [pid 3228 on line 48 of "/opt/local/www/apache2/horde/vendor/horde/rpc/lib/Horde/Rpc/ActiveSync.php"]
2026-04-13T15:34:43+10:00 DEBUG: HORDE Horde_Rpc_ActiveSync::getResponse() starting for OPTIONS [pid 3228 on line 197 of "/opt/local/www/apache2/horde/vendor/horde/horde/rpc.php"]
2026-04-13T15:34:47+10:00 NOTICE: HORDE Login failed from ActiveSync client for user horst. [pid 3228 on line 603 of "/opt/local/www/apache2/horde/vendor/horde/activesync/lib/Horde/ActiveSync.php"]
2026-04-13T15:34:47+10:00 NOTICE: HORDE Sending HTTP 401 Unauthorized header response. [pid 3228 on line 129 of "/opt/local/www/apache2/horde/vendor/horde/rpc/lib/Horde/Rpc/ActiveSync.php"]