New Exchange server, migrated domains and everything from SBS 2003 to Server 2012 and Exchange 2013.
No user is able to receive external email, I've verified that DNS on the exchange server points to the internal DNS server. The internal DNS server points to itself, but has the correct forwarders. Everything should work.
2012 Server Running Hyper-V
Host has on it as a VM: DC, Exchange, RDS servers.