Email deliverability: ensuring that the mail server reputation for one domain is not affected by that of another domain on the same server (on a Windows server if possible -- otherwise Linux)

Okay put in simple terms, I operate a few different websites and I may put them all on the same dedicated server but I want to make sure that the mail server reputation for one is not affected by any of the others.  I want each domain to have it's own unique SMTP server, or at least appear so to receiving email servers.  So for example, suppose I have these three websites hosted at these three domains (each with a unique IP address), with SMTP server IP/hostnames being the same as the website IP/hostname:

website:   SMTP server: the same (
website:   SMTP server: the same (
website:   SMTP server: the same (

Furthermore, I don't want receiving mail servers to know that these websites or SMTP hosts are on the same machine, because I want to make sure that the mail server reputation for one domain cannot be affected by the mail server reputation of any of the other domains.

Is that possible on a Windows server?  And if not, is it possible on a Linux server?

I won't be using IIS for SMTP (IIS won't do this properly anyway).  So I tried both Alt-n MDaemon and Icewarp MerakMail and not only added the other domains but also set it to bind each domain to it's IP address and so on.  But the email headers for emails from and still show a trace of, in this part of the email headers (I'll show it from both MDaemon and MerakMail):


Alt-n MDaemon, sent from through SMTP host:

Received: from ([ipaddressB])
  by with ESMTP; 16 Apr 2010 04:14:55 -0700
Received: from u1698465 by (MDaemon PRO v11.0.0 trial)
      with ESMTP id md50000000059.msg
      for <>; Fri, 16 Apr 2010 07:14:59 -0400

[Notice is there -- I don't want it to show at all since this is sent through the SMTP server for]


Icewarp MerakMail, also sent from through SMTP host:

Received: from domainB ([ipaddressB])
  by with ESMTP; 18 Apr 2010 04:24:31 -0700
Received: from u1698465 ([ipaddressB])
        by (IceWarp 10.0.8) with SMTP id APQ88925
        for <>; Sun, 18 Apr 2010 07:24:25 -0400

[Notice is there also -- again, I don't want it to show at all since this is sent through the SMTP server for]


(By the way ipaddressA (for is also the machine IP address, if that matters.)

I figure that if there's any trace whatsoever of or ipaddressA in the headers of the emails sent out by the SMTP for the other domains, then there's a chance that the mail server reputation for one domain/IP can be affected by the mail server reputation of one of the other domains/IPs.  Am I right?  And if so, what can I do?  Will I have this problem no matter what as long as they're hosted on the same machine?  And if so, what if I use separate VPS's (instead of actual machines), will that work just as well as separate machines?  

And is the story for Unix/Linux any different? Or would Linux SMTP implementations behave the same as in my Windows examples above?

I understand about DKIM and SPF/SenderID and how all that helps with deliverability but I still want to keep the reputations separate and independent, so please advise me on that.

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Psalmist777Author Commented:
Oh I should have added:  I'm talking about sending out server emails from each domain via PHP.  The examples I gave were sent using the standard PHP mail() function.  (I wonder if something like PHPMailer could solve my problem as well since it provides different ways to make the outgoing connection.)
Justin OwensITIL Problem ManagerCommented:
  • Question: Is this possible on a Windows Server?  Yes.
  • Question: Will this affect mailflow? No.
You are comparing apples to oranges.  Mailflow is controlled by the public MX record.  If the MX record is still pointing to the correct mail server, you are golden.  IIS name registration should not affect the MX record at all.  Windows IIS can handle (host) as many different websites as it can physically handle (I/O, storage, etc).

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