Varun Varma wrote:
What is so surprising is that all production mail systems have atleast one backup MX associated with them. I am sure that Suresh's book would cover that.
There's a growing school of thought which thinks this is redundant.
This post by Greg Woods on postfix-users does say a lot ... http://archives.neohapsis.com/archives/postfix/2002-02/0929.html
Typically, mail is retried for about 4 days. If you have mailserver downtime over 4 days you typically have far more than just a problem getting your mail.
<Quote for the post above>
Yes, in terms of giving better reliability the only time a secondary (or equal peer) MX is of any real value is if it's on a topologically different part of the Internet, and preferably also in a separate geographical location as well, even if that only means on a different floor with different power sources from the primary, but still in the same building).
</Quote>
In our case, the two servers are geographically and topologically separate - one is in Texas and the other in Michigan. The reasoning behind it is more than simple downtime - it's availability.
No co-loc provider at one place is going to peer with all possible ISPs and there are going to be broken ISPs on the client side, which peer better with one ISP than another.
If one were to compare email to telephones [which they are replacing, at least in part, for communication], then having backup MXs is like having a voice mail come up at the exchange when your telephone line is down so that people can leave a message, rather than get a message - "Yeh suvidha asthai rup se seva mey nahi hai." [This service is temporarily unavailable].
-- Regards, Varun Varma --------------------------------------- Mindframe Software & Services Pvt. Ltd. http://www.mindsw.com ---------------------------------------
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