I have an Active Directory and a Zimbra server on another machine. The domain I have on the active directory is myintranet.edu, and my domain on my zimbra machine is mydomain.edu.
So I had a gal error at first, so I created an external GAL with this command

zmgsautil createAccount -a galsync@mydomain.edu -n ExternalGAL --domain mydomain.edu -t ldap -f _ExternalGAL

So then I opened the GAL configuration wizard,

GAL Mode: External
Server type: Active Directory
ldap:// port 3268

On LDAP search base I had : mydomain.edu and I changed it to myintranet.edu

On GAL search settings I used:
Bind DN:cn=Administrador,ou=Usuarios,dc=edu
Bind PASSWORD=****** -> The administador user password.

I checked Use GAL search settings for GAL sync. (I am not sure about this part)

I created a user an it seemed to connect. I can see the user jdc created on zimbra but not on my Active Directory, do I need anything else?