That's why we are bought two M and C series appliance's. M series appliance can be configured work with "redundance" by "secondaryconfig" command - it gives you a backup of logs and reporting data. Aslo you can make a content filter to duplicate spam...
We sign all outbound mail with both DKIM and DomainKeys for all our domains. I test it with yahoo, gmail and some online tools like this http://www.myiptest.com/staticpages/index.php/DomainKeys-DKIM-SPF-Validator-testSerious guys must use DKIM (DK) a...