Authentication on trusted domain

[lfasci]

Hi

I have two trusted active directory domains: domain1.lan and domain2.lan
I need to set authentication for zimbra accounts on one active directory
domain controller (the one for domain1.lan) because the the domain controller
for domain2.lan is in another country.

I need to domain1.wan to autenticate on domain1.lan and this works well
but I don't know how to autenticate domain2.wan on the server for
domain1.lan that has a trusted relationship with the one for domain2.lan.

How do I have to configure this ?

Thank you very much

Bye
Lorenzo