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SecondaryMX and SPAM issues

Discussion in 'General Discussion' started by trich, Sep 26, 2007.

  1. trich

    trich Member

    Aug 8, 2006
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    We have two servers that are the primary and secondary MX for a number of our domains. On the secondary server, we just add the domain to the /etc/secondarymx file. We've been seeing issues with our Mail Queue on the Secondary MX server filling up with bounces from the primary server. What it looks like is happening is spammers are taking the secondary MX record and sending the SPAM to it. Then the secondary mx server sends it onto the primary MX server, the primary MX server detects it as spam and bounces it back to the place it came from (ie, the secondary MX server). Then thousands and thousands of messages continually queue up on the secondary MX server.

    Is there a way I can setup the secondary MX server to not accept bounces from the primary MX server? It is possible to put a condition in there, where it can only if the primary MX is down/not responding?

    Any help is appreciated.
  2. mtindor

    mtindor Well-Known Member

    Sep 14, 2004
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    Ideally you'd be able to do something in exim.conf on the secondary server to force it to do a callout to the primary MX in order to verify the existence of a recipient before it accepts mail for that recipient.

    Bad idea to have a secondary MX if the secondary MX does not know of the existence of the recipient beforehand - somewhere in the SMTP phase exim would need to do a callout to the primary MX to see if the account exists - then if it does, accept the mail for queuing, otherwise, reject it. And if the primary isn't available, the secondary would have to temporarily reject the mail until the primary was back up and could be queried for the existence of the users.

    I don't know if this has ever been approached in these forums before - but certainly Exim is capable of doing it if somebody writes up the proper stuff for exim.conf.

    Just shitcanning the bounces from the main server isn't a good idea - It would work, but it would also mean that in the event that a legitimate sender sent an email to a legitimate (but mispelled) recipient and the secondary MX handled that mail, the secondary MX would accept the mail, the sender would think the mail was delivered and would never receive notification that their legitimate (but mispelled) email was not delivered.

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