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On Thu, Jun 25, 2009 at 2:16 PM, Mick Vaites wrote: > If it's an internal MX then there is no reason why this box shouldn't have > knowledge of whether an email will eventually be delivered or not. > > However as we're talking ISP backup MX or Smarthost - they cannot drop > bounces on behalf of their customer as it might be needed genuinely. > > The only place that messages can be blackholed is by the person who's domain > is being attacked. If the two MXs work well together, the external one can be configured to regularly check with the internal one to see if certain addresses exist. It can do so during an SMTP transaction and, if the address doesn't exist, drop the connection. It's fairly common for MXs to work this way. Martijn. -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html