I have several postfix servers that send mail on behalf of my domain (example.com). When a from address is provided, DKIM and SPF pass properly. However, I noticed in my DMARC notifications there are a number of failing emails being send from my postfix servers.
Each postfix server maps to a subdomain in our DNS (smtp1.example.com, smtp2.example.com). Reverse lookups are configured at AWS for the sending IP.
When an email bounces, postfix sends the non-delivery notification email to the sender, but it comes from the null sender. These messages seem to fail DKIM AND sometimes SPF because they are sent from MAILER-DAEMON@smtp1.example.com and not MAILER-DAEMON@example.com.
What is the best way to go about managing this? Should I be creating DKIM AND SPF records for each subdomain? Is there a way to customize the mailer-daemon sender in postfix to have it sent from the domain and not the subdomain?
I figured out that in "/etc/postfix/main.cf" I need to change the $mydomain variable to example.com and set $myorigin to use $mydomain, but DKIM isn't being attached. I use OpenDKIM to apply DKIM to each outgoing mail, but because postfix uses from=<> instead of email@example.com it seems to skip it, though I'm not sure that is the reason.
I was able to get DKIM to be sent for bounced emails by adding "internal_mail_filter_classes = bounce" to "/etc/postfix/main.cf" as per:
I am still wondering if this is the best way to go about accomplishing my goal.
Bounced emails are sent from MAILER-DAEMON@example.com, but the recipient sees the email as sent from smtp1.example.com and signed by example.com. This requires I have another spf record configured for smtp1.example.com and I would prefer not to need this. Bounces should appear as sent by the root domain.
How do I accomplish this?
Adding email headers and output of
postconf -n. I have obfuscated the IP addresses and domain name only. The email was received by a gmail managed domain.
Delivered-To: firstname.lastname@example.org Received: by 2002:a2e:45d5:0:0:0:0:0 with SMTP id s204-v6csp753516lja; Wed, 26 Sep 2018 10:59:51 -0700 (PDT) X-Google-Smtp-Source: ACcGV62LaRKlAeJoVcCqIQRgHXwen7bLAev7n/gyBtIF7yWMLpmgBaL1q8D3Qm0zEMcDjPEmCjCz X-Received: by 2002:a0c:a9d2:: with SMTP id c18-v6mr54933qvb.191.1537984791474; Wed, 26 Sep 2018 10:59:51 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1537984791; cv=none; d=google.com; s=arc-20160816; b=0LNTMB+qiHPz1eHGcLyPLE1FcSmW30xptS1xcbd9Vmy1Wdx3/tg96AUrAeuoDSznHE b96zAG+sJHLASokmbete92FHI1G8rD8PgjH/IUCJ48Tl6fBZwkdKU7AGYAJ/2TTCBAuV V5qcBCIuomDpUVXLeDNYSpTPEpAtaUrm+l5S3wIkZXlyzTsEL9utiVdoKTmYNcyXzM53 afDdaokbJdrmm6h904P49QEgm1/76LVyjh3QvpzVmVkmz7bsRleBypROkS4GERE0UD87 ZVEKMlCkVw8y2lUJwx8OvYTIALGHLsrjHk3cICv8uCsCQleDeMK+Y7mxJ4og8isdmEJm aNTw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=message-id:mime-version:auto-submitted:to:subject:from:date :dkim-signature; bh=/kHg6GHVOA4im8+tNe6f5EdTttqwbtTK3EvxVBpLPe0=; b=VNuEQyKlo1YCgSBznYzBqNzJzJHaTqIxYzzEOhVfWH7KP4IdBvSQ5nwbigujfhq+a1 ch04W6nNbOaeTvC6hRdztL+Qw+lria0hOIx6eo3Hc8swQseAv6+iKh8hwbL4DM1tr84l wDmcPy808/tamGIBHacA1vhe7LU1ZWhaFmBcynllMaLXJDxDsJuZc2pAfQe3cu+1da0h twdEY+fYo8tVlVC/A0fb6iedP57tYygfg1LMSZhOxqwWiFDuNsOOn2Px0geyYcHWiyTj uZEtS4L1nfYr2J2tbeZsHMzrjPkM4etZMK52duSiNpMZnV0CN4dioHQcSskrik8Jgnmh Ki/g== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass email@example.com header.s=example header.b="Kh/wMFFv"; spf=pass (google.com: domain of firstname.lastname@example.org designates <IP-Address> as permitted sender) smtp.helo=smtp1.example.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=example.com Return-Path: <> Received: from smtp1.example.com (smtp1.example.com. [<IP-Address>]) by mx.google.com with ESMTPS id 144-v6si4528390qkh.294.2018.09.26.10.59.51 for <email@example.com> (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 26 Sep 2018 10:59:51 -0700 (PDT) Received-SPF: pass (google.com: domain of firstname.lastname@example.org designates <IP-Address> as permitted sender) client-ip=<IP-Address>; Authentication-Results: mx.google.com; dkim=pass email@example.com header.s=example header.b="Kh/wMFFv"; spf=pass (google.com: domain of firstname.lastname@example.org designates <IP-Address> as permitted sender) smtp.helo=smtp1.example.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=example.com Received: by smtp1.example.com (Postfix) id 1CEE260DBC; Wed, 26 Sep 2018 17:59:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=example.com; s=example; t=1537984791; bh=DalucSR/izsrTI/4cwdDwKrGi8R0OywUerOF7byykLI=; h=Date:From:Subject:To; b=Kh/wMFFvEE/uPx/7qKnYVZZACU6zzLl9S+Jwr1hXSBhIg0mfkqpVXgxvhUxqNkJXw xIPvmuJU9ERlA5RqT+xUC3y4kkxIbig6gBogUEFtOkbp1bNj+yWEKxcFpHJXEnDneP Na3dzhGZScaUK83sKEPMFkjubyiPR/6uoc5zcEVc= Date: Wed, 26 Sep 2018 17:59:51 +0000 (UTC) From: Mail Delivery System <MAILER-DAEMON@example.com> Subject: Undelivered Mail Returned to Sender To: email@example.com Auto-Submitted: auto-replied MIME-Version: 1.0 Content-Type: multipart/report; report-type=delivery-status; boundary="DF7BD600B7.1537984791/smtp1.example.com" Message-Id: <20180926175951.1CEE260DBC@smtp1.example.com>
alias_database = hash:/etc/aliases alias_maps = hash:/etc/aliases bounce_notice_recipient = firstname.lastname@example.org command_directory = /usr/sbin config_directory = /etc/postfix daemon_directory = /usr/libexec/postfix data_directory = /var/lib/postfix debug_peer_level = 2 html_directory = no inet_interfaces = localhost inet_protocols = ipv4 internal_mail_filter_classes = bounce mail_owner = postfix mailq_path = /usr/bin/mailq.postfix manpage_directory = /usr/share/man milter_default_action = accept milter_protocol = 2 mydestination = $myhostname, localhost.$mydomain, localhost mydomain = example.com myhostname = smtp1.example.com myorigin = $mydomain newaliases_path = /usr/bin/newaliases.postfix non_smtpd_milters = $smtpd_milters queue_directory = /var/spool/postfix readme_directory = /usr/share/doc/postfix-2.6.6/README_FILES sample_directory = /usr/share/doc/postfix-2.6.6/samples sendmail_path = /usr/sbin/sendmail.postfix setgid_group = postdrop smtp_tls_security_level = may smtpd_milters = inet:127.0.0.1:8891