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  1. #1

    MX Priority Question

    I understand how MX works and the different priorities, less is preferred and how can this be amazing for fail over.

    Example
    mx1.host.com 10
    mx2.host.com 20

    But... what is the difference for MX2 if it is 20 or 100? Or if MX1 was 5 instead of 10?

  2. #2
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    It's just a matter of preference. Personally I do mine starting from 0.
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  3. #3
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    It doesn't matter what the actual numbers are - only the order they sort the servers into is significant. Mail is sent to the lowest priority server that is contactable regardless of the intervals between the numbers.

  4. #4
    And if they had the same priority the DNS is balanced in a Round Robin style?

  5. #5
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    Quote Originally Posted by andretenreiro View Post
    And if they had the same priority the DNS is balanced in a Round Robin style?
    Yes, the MTA doing the delivery is supposed to pick one of the two with the same prefernce at its discretion. If delivery fails to that one, it should use the other at the same preference level and if delivery fails there, it proceeds to the next highest.

    I use suppose and should above because that is how the DNS component of the implementation was envisaged, however like all such things, if the software developer of the MTA doesn't design it that way, it wont be handled that way.

    The MX value assigned is a preference assigned by the system owner. The idea is that you assign your best/most reliable mail exchanger at the lowest level and less reliable/favourable ones higher up.

    As mentioned by other posters, the actual values don't really matter, just the order. Although having said that, if you choose a level 0, clearly you can't assign something better in future with out rearranging DNS settings (which carry a propagation penalty). Setting your current best at the lowest of 10 for example allows you to easily slot in another 9 better ones seamlessly and with no worries about stale DNS records.
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