My scenerio is
" php application---->Load Balancer----->smtp server...>relaying
My load balancer receiving mails from php application from different domains now for DKIM we need to sign by DKIM keys for each domain. this is very difficult to implement but now.. I want that when my smtp(multiple) relay mail it sign outbound mails by its own Domain keys for all outbound mails which are from different domain..?