Hi guys... I am actually puzzled on this one.. availability service in exchange 2007 can be configured in an untrusted forests topology Microsoft says. Then it says you need to configure galsync in order to synchronise the GAL between the two forests, so Forest1 mail enabled users will appear in forest2 as contacts so you can look them up and view F/B information. But how you supposed to use galsync and MIIS in an untrusted forest topology? Because availably service without galsync is useless as you can not look up users without galsync, and galsync needs a two way trusts. is there anyways you can have galsync without a two way trusts? If not.. then whats the point that availably service works on untrusted topology? Shaggy

this was the answer: trust not needed!! You don't need it installed in both forests. You can do it with a single server running IIFP.