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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.

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In short: MailChimp and other mail providers request/require that their customers include certain settings in the DNS records (DKIM & SPF records) of the customers domains that will authorise the mail providers servers to send messages on behalf of those customers.

How to set up DKIM and SPF for your own domain(s) is well documented, once you have done that will probably quite obvious how to use those settings efficiently for other domains that you host. If not, that is a different question altogether.

mailed by SERVERNAME, encrypted with TLS

That is quite simply what happens when the SMTP connection from the sending mail server to Gmail's incoming is encrypted with TLS. You govern that with the smtp_tls_security_level in Postfix. smtp_tls_security_level = may is usually best.

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  • Thank you for reply. What i mean: mailchimp or other SMTP service can send mail signed by their domain but with the headers FROM and REPLY-TO of my domain without adding any DKIM OR SPF over my domain DNS SETTINGS and the email is not going to spam foldrler. I've read in other posts that opendkim have to sign, with my domain, email behalf other domain(s). There's a funzion or something that i can use to sign email and the change from header with the domain of my customer for example? What i want to do is a newsletter system where my customers can send emails with my SMTP server using their dom
    – Simon D.
    Aug 15, 2018 at 0:33
  • More info: i've figured out that mailchimp uses relaxed/relaxed and in original message there's a bounce that indicates their server. Also uses in txt record for dkim the d= and the h= . Means something,? There's a way to sign email than send with different header but already signed in postfix? Or i have to configure something else? Thanks
    – Simon D.
    Aug 16, 2018 at 1:25

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