Utilizing multiple mail servers w/ sendmail


I'm wanting to setup a second mail server that will queue messages that weren't able to be received by the primary mail server because it was too busy.  I'm really looking for info on how most people set something like this up, configuration and just an overview.  Thanks.
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Very simple.  Configure your DNS to have two MX records- one for your primary (we'll call it a.foo.com) and one for your secondary (b.foo.com).  In your BIND setup, it'll look something like this:

    IN    MX     10      a.foo.com
    IN    MX     100      b.foo.com

Then, setup sendmail as follows: a.foo.com is responsible for a.foo.com and foo.com (I assume you already have this set up properly, since you said you want to add the second server).  b.foo.com is responsible for just b.foo.com.  When mail is unable to be reached @a.foo.com, the sending mail server will automatically retry using b.foo.com.  When b.foo.com recieves the mail, it will attempt to deliver to a.foo.com.  If it fails, it will see that itself is the second host, and continue queueing the message.  The two important things to remember is to make sure b.foo.com is NOT responsible for a.foo.com or foo.com (I mean, don't define it in the Cw macro), otherwise it will try to deliver locally. Also, make sure that b.foo.com is not a CNAME to another machine, but rather, that machine's true hostname.  I hope this helps, and if you have any more problems or questions, feel free to email me @ mzito@wwprsd.mercernet.net

Best Wishes,
Matthew Zito

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