I have tied down my exchange 5.5 (sp4) server to prohibit open relays by doing the following:
In the Exchange IMS Routing properties, checked "Reroute Incoming SMTP mail".
I then added to the "Routing" field ourdomainname.com and <inbound> as the destination.
In IMS Routing Restrictions I have checked "Hosts and Clients that successfully authenticate".
On an Outlook Express client I then created the appropriate smtp and pop3 domain info, and added the user accoutn info for both smtp and pop3 services.
Outlook Express POP3/SMTP clients may now authenticate and retrieve email, and send email, but only to ourdomainname.com (internal) addresses. Messages sent to any external addresses get a 550 Relaying is Prohibited message.
Desired result: I want my corporate clients to be able to connect to their exchange accounts remotely using Outlook or Outlook Express, and be able to deliver messages to any email address, internal or external.
Based on everything I can see, this should be working, but it's not.
Any suggestions would be greatly appreciated.