[CentOS] one server handled sendmail added two more servers messes things up

Les Mikesell lesmikesell at gmail.com
Fri Jan 1 20:29:26 UTC 2010

Jerry Geis wrote:
> All three machines have the same FQDN.
> something like A.mydomain.com, B.mydomain.com, C.mydomain.com
> The IP numbers are X.Y.Z.170, .171 and .172
> All three machines have MX records. they all have the same domain name.
> It is a big deal to request changes from the provider so I was hoping 
> there was a way
> to just tell the two new machines that incoming email to them just send 
> on over to the the
> first machine.
> Is there a way to do that - or am I going about this the wrong way?

You can forward by setting MAIL_HUB but it may cause problems where you accept 
mail at the rely, then reject at the delivery host because the user name is 
wrong or from spam checkes.  In that case, the intermediate host is required to 
construct a bounce message and try to deliver it - and for spam it probably 
won't be deliverable.

If you have some reasonably small number of users, you can make an alias file 
that forwards each user to the fqdn of the delivery server.  Or you can use a 
virtuser table for the same purpose with a default reject rule.

Or, as someone else suggested, just stop sendmail or block port 25 on the one's 
you don't want to work.  Outside deliveries will retry each MX until one 
succeeds, but it is slightly antisocial to knowingly make them do this extra work.

   Les Mikesell
    lesmikesell at gmail.com

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