I know that this topic has been discussed several times but I want to describe a very specific setup with a surprising solution (at least surpising for me).
I have a Zimbra server that services about 100 domains of different customers. Often a customer has more than one domain. Such a customer wants a GAL that covers all of his domains. I know that it is possible to set the GalSearchBase to "root" - but this is not a option, as the GAL should not cover all other (90+) domains.
What I did in the past was to set the zimbraGalMode to "both", create a galsync account with 2 datasources. The first datasource is the internal gal of the first domain, the second datasource contains the entries from the 2nd domain synced through ldap (ldap server is the zimbra server itself).
This works, but I always considered it to be a somewhat nasty setup (as you have to configure the ldap password of the zimbra server in the datasource).
Now I found out by coincidence, that you can specify more than 1 galsync account per domain. So if you want a combined gal for 2 domains, you could just configure email@example.com and firstname.lastname@example.org both to be the galsync accounts for domains1.com and domain2.com while both galsync accounts only have one internal datasource.
I could only do some brief testing with ZCS 7.1.0 (NE) but it seemed to be working fine. I don't know if there are any problems with ZCO or Zimbra Desktop.
Does someone know, if this is a supported setup? The question is: is this a feature or a bug :-)