On the Exchange 2010 side, you need to create a new Receive Connector: Exchange System Manager -> Server Configuration -> Hub Transport -> Receive ConnectorР”Р„dd a new one by right-clicking the frame and selecting 'New Receive Connector'. For Postfix, it's defining relayhost in /etc/postfix/main.cf. For Sendmail, it's a matter of uncommenting the 'dnl' line related to the SMARTHOST entry in /etc/mail/sendmail.mc, and defining an address. The approach I take to enable a dumb server/device-to-server relay like what you're looking for is to enable the smarthost on the Postfix or Sendmail system. I still may need the smarthost funcationality, though. Same for other devices that may need to relay (copiers, monitoring systems, etc.). I usually don't have my Linux and internal servers authenticate to the Exchange server if they're on the same network. the messages submitted by the Postfix box must not be rejected as spam even if they look like spam.Exchange must allow the Postfix box to send messages to any destination.

setting up an IPsec tunnel seems overly complicated for what should be a trivial Exchange configuration.

I would like mutual authentication (the Postfix box knows it's talking to the Exchange box and not a man in the middle Exchange knows that it is talking to the Postfix box).

I would like the email traffic between the two to be encrypted.

the postfix mail server is at a remote site with a dynamic IP address, so authenticating by IP address won't work.

That option doesn't feel right - it seems like there should be way to do server to server authentication, not just client to server authentication.

I guess I could add a standard user with a mailbox on the Exchange box, then configure my postfix box to log in to port 587 to relay mail. How should I set up authentication on the Exchange 2010 system? I have administrator access to the Exchange 2010 system, but I'm not very familiar with it. This is used to ease the management of a single mail server with aliases, security, and Internet access rather than maintaining numerous local mail servers.I have a postfix mail server that should relay all outgoing mail to an Exchange 2010 server (the Exchange box is my smarthost). When a host runs its own local mail server, a smart host is often used to transmit all mail to other systems through a central mail server. Whatever the reason for the 'poor reputation' or 'blacklisting', they can choose to redirect all their email out to an external smarthost for delivery. This could be because that IP was assigned in the past to someone who sent spam from it, or appears to be a dynamic address such as typically used for home connection. Sometimes, even if outward port 25 is not blocked, an individual or organisation's normal external IP address has difficulty getting SMTP mail accepted.

Instead, often they will set up a smarthost to which their customers can direct all their outward mail - or customers could alternatively use one of the commercial smarthost services. In an effort to reduce email spam originating from their customer's IP addresses, some internet service providers (ISPs), will not allow their customers to communicate out directly with recipient mailservers via the default SMTP port number 25.

Exchange 2010 smarthost