BTW, I'd like to note that several user dbs are already possible, with e.g.:

SOGoUserSources = (
{
type = ldap;
....
canAuthenticate = YES;
displayName = "GAL";
....
id = directory;
isAddressBook = YES;
},
{
type = ldap;
....
canAuthenticate = YES;
displayName = "GAL";
....
id = additional;
isAddressBook = YES;
}
);

Probably, only different ids are needed for this to work.

First, when reading this bug report, I thought having multiple user dbs would impossible currently, and this feature would need to be implemented.

But, actually, it turns out that only the part about separating the db into the password and user parts was an unimplemented requested feature.

(dovecot's configuration in this respect seems to be more flexible, of course, and perhaps, clear, because it allows different explicit kinds of merging several user dbs with the "skip", "result_success", "result_failure" parameters. I thought about suggesting defining several SOGoUserSources in your case, so that their results are merged, but then thought that it's not clear how the merging would happen, and it's not clear how to merge exactly the way you need.)