In our environment we have two Zimbra servers, one OSS and one NE.
incoming e-mail sent to an NE user flows like this;
outside user sending mail -> mx0.company.com -> mx1.company.com -> NE-recipient
I think the best approach to train primary and secondary would be to set up an alias to forward to both spam.randomStuffHere's. Users submitting spam train both the primary mx0 and secondary mx1 server to keep the balance. This would also be applied to ham, thus hamming it up .
Just curious if and how anyone else has done this.