Allow use of mailAlias from openLDAP instead of AD proxyAddresses

We're using an openLDAP server with PostfixBookMailAccount schema (https://github.com/variablenix/ldap-mail-schema/blob/master/postfix-book.schema).

For defining mail aliases the multi-value attribute mailAlias is used. However, currently the plugin only allows the usage of proxyAddresses from Active Directory.

Is it possible to add support for other alias attributes, too?