Apple have now self contained most of the config files for it’s services in the /Library/Server folders.
To make a mailing list you need to edit files in /Library/Server/Mail/Config/postfix
The file you need to edit is virtual_users
The format is
email@for_mailing_list.com Localuser1,Localuser2,localuser3
afterward you must postmap this file
postmail /Library/Server/Mail/Config/postfix/virtual_users
If you want to use an LDAP group try this :-
1. Use Directory Utility to add the field “EMailAddress” to the group considered, and specify the group email address in this field.
2. Create a file /etc/postfix/ldap-groups.cf or /Library/Server/Mail/Config/postfix/ldap-groups.cf and edit it with the following content (where server01 is obviously the name of the server):
version = 3
server_host = localhost
search_base = cn=groups,dc=server01,dc=pretendco,dc=net
query_filter = (mail=%s)
result_attribute = memberUid
result_format = %u@pretendco.net
3. Test the configuration by typing
postmap -q (EMailAddress)@pretendco.net ldap:/etc/postfix/ldap-groups.cf
where (EmailAddress)@pretendco.net is the group email address. You should see a list of the users belonging to the group.
4. Edit the file /Library/Server/Mail/Config/postfix/main.cf and put the following two lines at the end
virtual_maps = ldap:/etc/postfix/ldap-groups.cf
virtual_alias_maps = $virtual_maps
5. Restart postfix
sudo postfix reload