Linux – Simple SMTP server which can redirect all mail to single address

Not only possible, but easy :-)

Unfortunately I haven't got a server to hand with just the SMTP service on it (only Exchange and this messes with the SMTP config interface). From memory if you go into the SMTP server config you can add domains and for each domain you add you configure the mail delivery. The domain can be local, in which case the mail is stored on your server, or remote. For remote domains you can configure the mail to route to a different server.

So you just set up a domain myinternaldoamin.com as a remote domain and configure the mail to deliver to your "real" mail server.

JR

Edit:

The Windows SMTP server can't modify mail headers. It can only pass on mails unchanged. However the Windows SMTP server allows you write event sinks. These are bits of VBScript that get executed whenever mails pass through the server, and from this code you can make any changes you want to the e-mail. This is often used to implement a catchall mailbox, as neither the Windows SMTP server nor Exchange 2k/2k3 provide this. I would be wary of writing synchs for production servers as you have to make damn sure there are no bugs in them and you document them thoroughly. However for the use you suggest they should be fine.

http://support.microsoft.com/kb/324021 is a good place to start. This describes writing a catchall script for Exchange, but you should be able to adapt it for your requirements.

JR

Howewer you configure it, Exchange is not going to route a message outside the organization if the destination address belongs to someone in Active Directory. Whenever Exchange needs to route a message, the first step it tries is always to look for the destination address in AD, and only after this fails it will choose a proper external routing path, based on the connectors you define.

With Exchange 2007 you can have "shared" SMTP domains, i.e. domains for which some addresses may be managed by Exchange, and some other by another system (in a coexistence scenario); I don't know if/how this is possible with 2003, but even if it was, the above stated golden rule still applies: first thing first, Exchange will try to deliver the message internally, and only if it can't, it will send the message outbound.

Think about it: if there was a way to do what you ask, what would Exchange do when receiving a message for a given user (even if it was already being forwarded by your provider)? It would route it back to your provider. There is no way to route messages based on who sends them, only on their destination; and the destination would be the same when the message is coming from Exchange itself, or when is coming from outside: if your wish could come true, you'd be stuck in a mail loop.