Fresh univention install with Kolab Enterprise without updates:

If I create a new user with email/kolab enabled

univention-directory-manager users/user create \
    --position "cn=users,dc=mycorp,dc=com" \
    --set username="juser" \
    --set firstname="joe" \
    --set lastname="user" \
    --set organisation="World Domination Corp" \
    --set mailPrimaryAddress="joe.user@mycorp.com" \
    --set password="securepasswd" \
    --set mailHomeServer="mail.mycorp.com"

it works as expected, I am able to login into kolab webmail.
After updating to the current/latest errata and creating a second user jsmith with john.smith@mycorp.com I am not able to login into kolab webmail with this particular user, the old one still works.
If I create a user john.smith with john.smith@mycorp.com I am able to login again.