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MX records with same priorty?

Discussion in 'Data Protection' started by pratapsingh, Mar 25, 2009.

  1. pratapsingh

    pratapsingh Active Member

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    I've set two MX records with the same priority in my zone file.
    How will it work ? Will both be checked simultaneously ? please explain how I could prioritize Mail servers ?
     
  2. nwilkens

    nwilkens Well-Known Member

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    You may want to refer to http://en.wikipedia.org/wiki/MX_record and other searches for "MX Priority".

    From wikipedia: .. "the lowest-numbered records are the most preferred. This phrasing can be confusing, and so the preference number is sometimes referred to as the distance: smaller distances are more preferable."

    When two MX records have the same priority the sender SMTP server selects a random MX record of the two.
     
  3. pratapsingh

    pratapsingh Active Member

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    full description for that

    Same Priority number for MX servers

    -->>When the preference numbers are the same for two MX servers, they have the
    same priority, hence those two terms are used interchangeably.

    To provide reliable mail transmission, the SMTP client must be able to try
    (and retry) each of the relevant addresses in this list(RR records or zone db
    file) in order, until a delivery attempt succeeds. If there is more than one
    MX record with the same preference number, all of those must be tried before
    moving on to lower-priority entries.

    Basically this is basically used for load balancing, if you own
    that (backup, other mail server) server too.
    Otherwise there are many reson to do not assign the same priority number to MX
    records, those reason are here

    * * *the backup server is owned by a different company or organization
    * * *the backup server does not have direct access to the primary mail * *
    storage
    * * *the backup server cannot determine valid recipient addresses
    * * *the backup server's Internet bandwidth costs more
    * * *the backup server has significantly less Internet bandwidth
    * * *the backup server has a high-latency Internet connection

    *
    And, they will not be checked simultaneously, the DNS server is free to
    carefully manipulate its balancing based on any method, including round robin
    DNS, mail server load, or some undisclosed priority scheme.

    Assigning the same preference value to all of the available servers provides
    the same benefit and may even help avoid overload situations and thereby
    increase system throughput by decreasing latency.

    If you want to prioritize your MX records Then assign the lowest number to
    preferred mail server and highest number to backup server.
     
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