Can't send mail from one hosted domain/user to another on Exchange 2010 SP1 hosting server

My problem is:

I have a Exchange 2010 installed in hosting mode.
I have 6 companies using this server with 6 different domains. The users of each domain can send and receive emails from and to domains on the internet.
The problem is that they cannot send to each other, e.g. sends a email to, the mail dont get through and the following error is received:
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##
I rember at some point having made a change so this was working for the first domains that I created a long time ago, but I just not able to find how I did in my notes, so this is a problem everytime I create a new company/domain, :-(
The 2 first companies that I aparantly fixed this on are not able to send to the new domains either, but they can still send to each other.
Who is Participating?
MrbonnAuthor Commented:
Found the solution here!!
The command:
new-SendConnector -Name 'TestOrg' -Usage 'Internal' -AddressSpaces ';1',';1' -IsScopedConnector $false -DNSRoutingEnabled $false -SmartHosts '[]' -SmartHostAuthMechanism 'None' -UseExternalDNSServersEnabled $false -SourceTransportServers 'Exchange'
I think you may need to set up a separate send connector for the Internal domains so that the mail gets routed internally.

See the follwing article which may help:

MrbonnAuthor Commented:
I have tried this, and it dosent seem to do the trick, still getting the same error.
550 5.1.1 RESOLVER... .... .... ..
MrbonnAuthor Commented:
Found a solution via the mentioned link!
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