On Mac OS X Lion (This also apply to all later versions of OSX), while connected to VPN, I was not able to resolve hostnames on a remote site. The solution was to create domain resolver files in /etc/resolver named for the different domains the I wanted resolved, for example:

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sudo mkdir /etc/resolver

vi /etc/resolver/yourdomain.com

Add the following content and save the file:

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nameserver x.x.x.x <- the DNS server to resolve hosts for yourdomain.com
domain yourdomain.com
port 53

You can create as much as needed custom domain resolver files, one for each domain.