Hi,
the file /etc/postfix/tls_policy.db should exist, if the update succeeded. Please check if there were errors in /var/log/univention/updater.log
To continue an interrupted installation/update run apt-get install -f
If there is a file /etc/postfix/tls_policy but not /etc/postfix/tls_policy.db, then you can run
postmap /etc/postfix/tls_policy
to create it.
When the situation with the tls_policy(.db) file has been resolved, please return the UCRV mail/postfix/tls/client/level to its default:
ucr unset mail/postfix/tls/client/level
Greetings
Daniel Tröder