Mail server with multiple IPs - Header info shows the wrong IP

Posted on 2006-05-23
Last Modified: 2008-03-03
We have a mail server that has multiple real IPs assigned to a single card.  For this docuement i will refer to them as IP1 ( and IP2 (  All internal users get to the machine on its primary ip (IP1) because accessing it via name resolves to this address.  All mail functions are setup to only work on IP2, a netstat does confirm that 25 and 110 are only running on the IP2 interface.  Also our external DNS has the correct IP2 number for the MX (the MX points to an alias which in turn is IP2).  The internal machine is called internal.domain.local.  When i send a message outbound and rip the header apart i find IP1 in the header information.  This is causing serious issues sending mail to places like and since they do a full RDNS trace back to your mail server.  They are getting IP1 which has no MX or RDNS and not IP2 as the server is setup to do.

I feel like i am just missing something here, but another set of eyes might help.  Any suggestions?

Please send responses directly to me at <email address removed by sembee>
Question by:caimis
    LVL 104

    Expert Comment

    Exchange uses the default IP address for all communications. You can set as many IP addresses as you like (I have an Exchange server at one client with 32 IP addresses) everything will go out through the default.

    LVL 1

    Author Comment

    The SMTP Server is not set to use all addresses though, only 1.  And netstat shows that to be the only IP in the system with port 25 open.

    LVL 104

    Accepted Solution

    Unfortunately those settings don't really matter. That just means the server is listening on those ports. The traffic still comes out of the main IP address of the server.

    I have been through the same thing with a client a few years ago.
    The only way to get the email to come out of a second IP address is to use a second NIC and then bind the SMTP service to that NIC/IP instead.

    LVL 1

    Author Comment

    Annother awesome feature by Microsoft, i say feature because they dont have bugs.  Doesnt seem to really be a point to putting that field in there if its not really useful.  Thanks for your answer.


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