At work we have one server running Windows Server 2003 SBS. This server is used as a proxy for Internet access; it also runs AD and Exchange.
We use a hosting company for our domain and they also collect our public email (POP 3) which is periodically collected by Exchange. Outbound email is relayed to BT. We do use OWA for external access to Exchange and this is achieved by a public IP address provided by BT. The FQDN of the internal server is simply a private local name.
My company has recently been purchased by another company who want us to use their domain name immediately. Thus I need a quick and safe solution. We have set up their new domain to relay email to our POP 3 provider in terms of relaying appropriate incoming email under their domain. This works fine.
However, it gets more complicated when setting the new domain as the primary email address for my internal users, as many spam filters do not like receiving email from one domain which originated from another and this is bad practice.
My question is how do I solve this in the interim? We will be fully integraing with their domain over the next few months but I need my users to be able to email from the internal network under the new domain domain quickly.