I have around 10 servers and all of them are running Postfix for web-hosting based clients. so I can only judge outgoing sender domain but not the destination domains. It can be anything.
now, I have placed a master SMTP Gateway on top of all these Postfix Servers and routed all other servers through the master SMTP Gateway. ( reason being to avoid handling 10 postfix servers and also hiding their information to avoid DDOS attacked, I am hiding as much information as possible by doing header checks rewriting)
Question:
Do I need to configure the DKIM on the Master SMTP Gateway server or on all individual servers...
Its a CentOS setup and I need some guidance on setting on the DKIM so that all outgoing emails are being signed and accepted by big emails guns like Gmail, Yahoo, and hotmail etc.