I've configured a SMPT server using postfix, dovecot, opendkim, openspf, openssl etc... I'm trying to figured out how mailchimp can send mails signed by their servers and deliver to recipients without going in spam folder. Same things with other external servers. When the example mail arrives in my gmail inbox, in details there are: Signed by SERVERNAME (not the same domain of sender), mailed by SERVERNAME, crypted with TLS. As i write before, the servername isn't the same of sender domain. So how can i configure postfix to do the same? Exactly how can i sign an email and then change the sender domain?
Sorry for my bad english. Thanks you all.