Cached mode gal not updating

I tried deleting the OST file but that didn't work. Can you try and run an Autodiscover test of the outlook client itself and see if it can reach it.

We had some of Outlook clients running a patch that was blocking access to autodiscover and in turn would not allow the users to get the OAB.

However, when they log into another PC and create an Outlook profile, the GAL is properly populated.To make new users show up in the GAL immediately, you can force a rebuild of the OAB.Once the OAB is rebuilt (may take longer in larger organizations), users must download the OAB in Outlook.Unfortunately, by default Outlook cached mode also includes the Global Address List.This can mean that new accounts or distribution lists are not available to all clients straight away.