Postfix rewrittes alias


I installed Kopano on Debian 9 as described in the Kopano Core Administrator Manual with Postfix and OpenLDAP. Everything seems to be working fine, except aliases. I created aliases for several users in LDAP and when email is sent to those aliases the to field gets rewritten by Postfix. So an email sent to is correctly delivered to, but the to field in the user’s inbox shows and not Is there any way to change this behavior so that the to field gets preserved for aliases?