[horde] Mail is not activated

[Ferdinand Gruber]

Hi,

after upgrade of horde using the command composer upgrade  I get the message

Mail is not activated

on line 1550 of 
"/srv/www/htdocs/horde/vendor/horde/core/lib/Horde/Registry.php"

Of course I have a backup of the old configuration. Seems that some 
configuration file must be edited manually ore copied back to horde from 
my backup.

Whar can I do? Please help!

-- 
Regards from Austria
Ferdinand Gruber