I have Ubuntu server running with bind9 and I have configured some forwarding ip addresses for dns
I also have the file resolv.conf where i have added the isp dns numbers

but I think i do it wrong and i need to create zones for dns lookup?

I also have another issue and that is that if i connect my mobile phone at home on wifi this works but if i want to sync the mails from my work it should go through another nameserver but this name is not found through the standard dns servers because it is an internal name on our work network.
Somebody told me to create some kind of forwarding zone in ubuntu that if i ask this name it should forward it to the ip address of our server at work through the existing vpn tunnel.

Can somebody explain how to create this forwarding rule/zone in the ubuntu server?

Chewing this over, and there may be other ways - but I'm lazy; Would it not be simpler to set up a local zone file in your bind server, so if a query is made for 'mail.my_company.internal' it just resolves the IP address for it? If this then turns out to be a non-routable private address I'm guessing adding a static route to push it down the VPN would be the fix for that aspect of it?

My knowledge is sketchy here so apologies if this is plain wrong:, but BIND does do 'views' where certain clients can be made to see the 'DNS stratosphere' in different contexts. I think this may include setting of different forwarders on a per 'view' basis. Perhaps this link: http://www.zytrax.com/books/dns/ch7/view.html would be a useful starting point?