How to Setup?

Well, since I didn't go to OU, I can say it: it's great having your particpation here, Jon! [;)]  Learning, teaching and helping - that's what this place is about!

The idea of the 'Relaying' tab is, "What SMTP traffic coming to me (the SMTP Proxy) am I allowed to relay?"  In an Exchange environment, this is usually just the Exchange server itself.  Having 'Transparent' enabled or including 'Internal (Network)' in 'Host-based relay' means that any infected PC can send thousands of solicitations an hour for your most-un-favorite Nigerian fraudster.

With only the host definition for Exchange in 'Host-based relay', the Proxy knows that that's the only source of SMTP it should accept for relaying, so, yes, that forces everyone to authenticate to the Exchange server.

Cheers - Bob

Hi Bob,

sorry for returning to this old thread, but I am a bit confused on the Transparent mode or not. Following the question from "JonEtkins" I also would enable Transparent mode to intercept all port 25 traffic - no hosts in "Skip Transparent Mode Hosts/Nets". Otherwise you will need to DNAT to the internal mail server.

Yes, only internal mailserver in Allowed SMTP hosts on the Relaying tab.

Am I missing something here?

/Claus, DK

Transparent mode isn't needed to avoid DNAT, Claus.  All SMTP traffic from the Internet that hits an Interface with a default gateway will be captured by the SMTP Proxy without Transparent mode.  SMTP traffic from the internal mailserver will be captured by the SMTP Proxy without Transparent mode.

In Transparent mode, the SMTP Proxy will also capture all SMTP Traffic that hits Interfaces without a default gateway.  This can allow infected PCs to spam the world and get your IP onto many RBLs.  I recommend using Transparent only for debugging purposes and leaving it off virtually all of the time.

Cheers - Bob

Transparent mode isn't needed to avoid DNAT, Claus.  All SMTP traffic from the Internet that hits an Interface with a default gateway will be captured by the SMTP Proxy without Transparent mode.  SMTP traffic from the internal mailserver will be captured by the SMTP Proxy without Transparent mode.

In Transparent mode, the SMTP Proxy will also capture all SMTP Traffic that hits Interfaces without a default gateway.  This can allow infected PCs to spam the world and get your IP onto many RBLs.  I recommend using Transparent only for debugging purposes and leaving it off virtually all of the time.

Cheers - Bob