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Adding an MX Record

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  • Adding an MX Record

    Hi everybody!

    We have a loadbalancer with a T1 and a DSL lines attached to it. Our DNS is hosted by Network Solutions. MX record is pointing to the T1 ip.

    Last night T1 went down, and messed up most Exchange communications. Incoming messages could not reach the Exchange box for several hours.

    Our DSL line has a static ip address. Can we just add an additional mx record pointing to the DSL ip with a lower priority, and create another port forwarding entry in the router to make incoming messages flow throught the DSL line in case T1 is down?

    Or is there something else we should be aware of? Personally, I think that this must work, but a little hesitant to do strange things on a production server.

  • #2
    Re: Adding an MX Record

    Yeah that will work.

    Just change the cost i.e. set the cost for the primary IP address to be 10 and the secondary to 11 (Or what ever numbers you want to use).

    Michael Armstrong
    MCITP: EA, MCTS, MCSE 2003, MCSA 2003: Messaging, CCA, VCP 3.5, 4, 5, VCAP5-DCD, VCAP5-DCA, ITIL, MCP, PGP Certified Technician

    ** Remember to give credit where credit is due and leave reputation points sigpic where appropriate **


    • #3
      Re: Adding an MX Record

      Thanks Michael

      I think so too.

      Good luck with the 298! It was not as hard as they tried to make it look. For me it was all downhill from the 291.


      • #4
        Re: Adding an MX Record

        I wouldn't actually recommend doing this as it will actually increase the level of traffic that the DSL line has to cope with.

        Spammers use the higher cost MX records if possible to send their messages, because in many cases the higher cost server does not have the same protection. People believe that the higher cost record will not be used in the event that the primary is available - which is not the case.

        Where there is a second line available, what my preferred method to do is to use a dynamic DNS Address. A new host is created and mapped to the same IP address as the original host name. The host is added to the MX records with the same cost. This means you have two MX records, both pointing at the same host.
        However in the event of a failure, simply change the DNS record with the dynamic DNS provider. The change will be live within minutes and email starts coming in on the other connection. When the real connection is back, switch them back.
        As you are changing the host IP address, not the MX record DNS entry, the 48 hour propagation time doesn't apply.

        Simon Butler
        Exchange MVP

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        • #5
          Re: Adding an MX Record

          This seems like a lot of DNS fussing to me. I would stick to your original idea of creating a second, lower priority MX pointing to the DSL ip address. While it's true that spammers will try to send to the second MX, legitimate email servers won't as long as the first MX is available. To combat the spammers simply shut down the SMTP service on the second email server and start it only if you failover to the DSL line. As far as bandwidth usage on the DSL line from spammers is concerned, it's probably negligible (think about how much of your T1 they're using right now sending to your primary email server). Besides, if you're not running on the DSL line then who cares if bandwidth is being used as it won't affect your production network anyway.
          Last edited by joeqwerty; 8th August 2007, 03:43.


          • #6
            Re: Adding an MX Record

            Thanks for your replies.
            I already added that backup mx record, and configured rest of the things.
            I do not have a second mail server or a server cluster. The idea was to point incoming mail to the dsl line, and then to my only mail server. It's true that spammers love backup mx records, but my mail traffic will still go via the same route, which has techniques to implemented to combat spam.
            Thank you again.