[exim] Exim and multi-value attributes

Hello,
I am trying to get iRedmail to work on a Samba4 AD server, I have
imported the iRedmail schema and testing it works except for getting
group members. Instead of storing the domain users under the domain OU,
I am storing them in the users DN in the 'otherMailbox' attribute

i.e.
instead of using dn:
mail=user@???,ou=Users,domainName=example.com,o=domains,DC=example,DC=com

the user lives in dn: CN=user,CN=Users,DC=example,DC=com

With multiple 'otherMailbox' attributes, if you do an ldapsearch group
search with the result attribute being 'otherMailbox', you get back all
the 'otherMailbox' in a users dn

For instance, if under dn: CN=user,CN=Users,DC=example,DC=com, you have:

otherMailbox: user@???
otherMailbox: user@???
otherMailbox: user@???

You would get:

user@??? user@??? user@???

So, you cannot do this with postfix, but can exim trim this list down to
one mail address based on the domain part of the initial search address

i.e. if you search for mailgroup@???, you would get returned
user@??? not user@??? user@??? user@???

A simple yes or no answer will do, if yes, I will install Exim and start
reading the documentation

Thanks

Rowland