How do you handle reverse DNS names for two email domain names?

Discussion in 'Windows Small Business Server' started by DrJonz, Aug 22, 2007.

  1. DrJonz

    DrJonz Guest

    Customer needs a second email domain name which I have configured in
    Exchange. They can receive mail fine on the second name. But for users to
    reply using that name, I need to setup a second IP mated to a reverse DNS
    name matching this second email domain or else they'll get lots of bounce

    I currently have the SBS server with one NIC behind a router which forwards
    MX to it. From this point, I don't know how to get the 2nd IP in the mix. I
    was thinking of a dual WAN router but even then, the server would reply over
    its gateway and 1st reverse DNS name.

    DrJonz, Aug 22, 2007
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  2. Hi,

    You don't need a second public IP for that other domain at all. You also
    don't need to change the reverse DNS. Simply point the MX record for that
    second domain to the public IP of your server. Add the email domain in the
    Recipient Policy.
    If a user needs to be able to have that second domain as primary, uncheck
    the 'Automatic update recipient policy' in the properties of that user.


    Marina Roos
    Microsoft SBS-MVP
    One of the Magical M&M's
    Take part in SBS forum:
    Marina Roos [SBS-MVP], Aug 22, 2007
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  3. DrJonz

    DrJonz Guest

    I'm that far already. But if I leave it like this and set a user to to use
    the second email as primary, won't the receiving server check the reverse DNS
    and see the name of the first email domain name and block it as spam?
    DrJonz, Aug 23, 2007
  4. DrJonz

    Gregg Hill Guest

    I am not certain, but would the second IP even be needed? Wouldn't you just
    be able to have your ISP set up a second PTR record for the second domain
    name, and have it point to the same IP as the first mail server name?

    For example, = IP address = same IP address as above

    Just a thought. I'd love to know how it will work, since I am about to do
    exactly the same thing.

    Gregg Hill
    Gregg Hill, Aug 23, 2007
  5. Marina Roos [SBS-MVP], Aug 23, 2007
  6. try this one

    What would happen if I ran both and, but the primary MX in
    public DNS for both was
    SuperGumby [SBS MVP], Aug 23, 2007
  7. No Gregg, You can't have two mx records pointing to the same IP for 1
    Each domain needs to have the MX pointing to the same public IP of the SBS
    server. And the name of that MX record should be the same for both domains.

    So if the MX for the first domain was setup with

    The second domain will have exactly the same MX record:

    The name doesn't really matter at all and can be about
    anything. As long as that name is pointing to the right public IP


    Marina Roos
    Microsoft SBS-MVP
    One of the Magical M&M's
    Take part in SBS forum:
    Marina Roos [SBS-MVP], Aug 23, 2007
  8. DrJonz

    bmason505 Guest

    Makes perfect sense. It helps to know how those checks work. And it's good
    news because it means I have nothing more to do than change the primary on a
    couple accounts. Thanks! And while I'm offering my thanks for this reply,
    let me say thanks to all who participate here because I've made good use of
    this site over the past year.
    bmason505, Aug 23, 2007
  9. DrJonz

    Gregg Hill Guest

    Wow. That never even crossed my mind, but makes sense now.

    Thank you for clarifying it!

    Gregg Hill
    Gregg Hill, Aug 23, 2007
  10. DrJonz

    stephen Guest

    PTR records are generally needed for the IP address of the server that's
    making an outbound connection to another SMTP server. This has nothing
    to do with MX records, because MX records are for inbound mail! (I know
    dnsreport tests MX records, but that's all it can do, and it's not
    really a valid test. I could have my MX record set to or
    exchangedefender for inbound mail scanning, but that's nothing to do
    with my outbound mail)

    The best practise for PTR records is:
    1/The external IP address of the server should have a PTR record that
    matches a forward A record for the server. E.g. has PTR for and has an A record pointing

    2/ Ideally, the SMTP HELO greeting of the server should be an A record
    that matches the PTR of the server. (The HELO greeting name is set in
    Exchange SMTP virtual server advanced delivery -> fully qualified domain
    name). SBS setup sets this to, but that's not necessarily
    correct as may point to your externally hosted website
    (i.e. it's set to the same IP as You really want to
    HELO greeting to say since the A record for that
    matches the server's IP. Some servers will reject your mail as as forged
    if the HELO greeting has an IP address different to the IP that's making
    the SMTP connection (postfix policyd_weight tests this for example).

    By the way, there is nothing illegal in having multiple MX records
    pointing to the same address. It's not sensible, but nothing will break
    by having:
    IN MX 5
    IN MX 10 IN A

    -- stephen
    stephen, Aug 23, 2007
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