I have a client who is running Xeams and just discovered a minor "DNS leak" in what appears to be the Xeams applied email headers. Whether sending to an internal or external address, this header is always attached (names changed to protect the innocent): 

  X-SM_ReverseDNS: speedtest.clientdomain.com clientdomain.com webserver.clientdomain.com roundcube.clientdomain.com

The reverse lookup is valid as the Apache server is hosting multiple applications, including the email application.
The problem is, we don't want/need all of these internal hostnames advertised in emails, especially to external recipients.
I've tried adding a static entry to /etc/hosts without success.

What can be done to either:
- Disable/Remove the X-SM_ReverseDNS header line
- Restrict the reverse lookup to return only a specific host (without modifying the DNS server entries, breaking other applications)

Env:
Xeams 9.0, build 6302
Ubuntu 20.04.6

Use the following method to disable this:

• Locate or create server.properties file. Check https://www.xeams.com/server-properties.htm for details.
• Add the following line:
  
  omit.reverse.dns.in.header=true
• Save
• Log out and log back into the web interface