I have an IIS 6.0 SMTP virtual server (VS) installed on-premises. I utilize this SMTP VS to relay email messages from internal applications to Exchange Online Protection for routing either to my Exchange Online tenant or external recipients. Some of the messages sent to this SMTP VS originate from on-premises applications which send messages with non-public SMTP sender domains. For example, an application might send an email message with the sender address of app1@domain1.local. I've been looking into solutions that rewrites these non-public SMTP sender domains from domain1.local to mycompany.com. From what I can tell, the "Masquerade Domain" features of SMTP VS should be able to adjust the Return-Path of the message header to the domain that I specify... unfortunately, through my testing its not working for me. I entered "mycompany.com" in the Masquerade Domain field, then restarted the server. After the server came back up I attempted to manually send an SMTP message through the SMTP server by using telnet and the following commands:
mail from:app1@domain1.local
rcpt to:test1@hotmail.com
data
Subject: App Test 9:22
To: test1@hotmail.com
.<CRLF>
QUIT
The result is that the message is delivered to the Hotmail recipient, but in looking at the message header the return path hasn't been modified. The following articles indicate that there may be some intricacies around getting Masquerade Domain to work, but its not clear to me what I'm missing. Can you please provide insight into what I'm missing here? Should this address rewriting work as I've implemented? The second article below indicates that "Masquerade domain setting works when the SMTP VS is a bridgehead for a Connector", does this mean that an Exchange infrastructure is required for this to work? I do not have any Exchange infrastructure on-premises.
https://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/0daa6ab7-ab48-4132-acf0-84de0db8c596.mspx?mfr=true
http://exchangepedia.com/2007/12/masquerading-smtp-virtual-servers-changing-the-fqdn-and-masquerade-domain.html
Thank you in advance!
ME