I want to enable SMTP authentication on my exchange server so that POP clients have to authenticate before sending mail, thus helping eliminate an open relay.
I've tried going in to Protocols>SMTP>Default SMTP Virtual Server>Access tab>Authentication button and unchecking 'Anonymous Access', which seems to work. Upon testing I found that no matter where I'm at, I have to authenticate to send mail from my Outlook client whether it's to an internal domain address or external. Which is what I wanted. However, through more testing, I noticed that with those settings in place, I can no longer receive mail from external sources.
I can trace the external mail coming in to our gateway, but log messages indicate that 'Client does not have permission to submit'. How can I accept incoming messages from my gateway server to my exchange server AND still require authentication for incoming messages from my SMTP clients?