{"id":847,"date":"2012-09-20T23:25:23","date_gmt":"2012-09-21T05:25:23","guid":{"rendered":"http:\/\/blog.supportpro.com\/?p=847"},"modified":"2026-03-26T23:53:18","modified_gmt":"2026-03-27T05:53:18","slug":"postfix-dkim-setup","status":"publish","type":"post","link":"https:\/\/www.supportpro.com\/blog\/postfix-dkim-setup\/","title":{"rendered":"How to Install and Configure OpenDKIM with Postfix for Secure Email Authentication ?"},"content":{"rendered":"\n<p>Email authentication plays a critical role in improving email deliverability and protecting domains from spoofing. <strong>DomainKeys Identified Mail (DKIM)<\/strong> adds a digital signature to outgoing emails, allowing receiving servers to verify that messages are legitimate and unaltered.<\/p>\n\n\n\n<p>This guide explains how to install and configure <strong>OpenDKIM<\/strong> with <strong>Postfix<\/strong> to enable DKIM signing on a Linux server.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What is OpenDKIM?<\/h2>\n\n\n\n<p><strong>OpenDKIM<\/strong> is an open-source implementation of the DKIM standard. It integrates with mail transfer agents like Postfix to automatically sign outgoing emails using cryptographic keys.<\/p>\n\n\n\n<p>Benefits include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Improved email delivery rates<\/li>\n\n\n\n<li>Reduced spam classification<\/li>\n\n\n\n<li>Protection against email spoofing<\/li>\n\n\n\n<li>Increased domain reputation<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Step 1: Install Required Packages<\/h2>\n\n\n\n<p>Install the <strong>RPMForge repository<\/strong> and required packages.<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>wget http:\/\/pkgs.repoforge.org\/rpmforge-release\/rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm<br>rpm -ivh rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm<br>yum install opendkim postfix<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Step 2: Disable Sendmail<\/h2>\n\n\n\n<p>Stop Sendmail and remove it from startup services.<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/etc\/init.d\/sendmail stop<br>chkconfig sendmail off<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Step 3: Enable Services at Boot<\/h2>\n\n\n\n<p>Enable Postfix and OpenDKIM services.<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">chkconfig postfix on<br>chkconfig opendkim on<\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Step 4: Configure Postfix<\/h2>\n\n\n\n<p>Edit Postfix configuration:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>vi \/etc\/postfix\/main.cf<\/code><\/pre>\n\n\n\n<p>Update or add the following parameters:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>myhostname = server.yourdomainname.com<br>mydomain = yourdomainname.com<br>myorigin = $mydomain<br>inet_interfaces = all<br>mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain<br>home_mailbox = Maildir\/<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">Add DKIM Integration<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>smtpd_milters = inet:localhost:8891<br>non_smtpd_milters = $smtpd_milters<br>milter_default_action = accept<br>milter_protocol = 2<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Step 5: Configure OpenDKIM<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Important Configuration Files<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><div class=\"pcrstb-wrap\"><table class=\"has-fixed-layout\"><thead><tr><th>File<\/th><th>Purpose<\/th><\/tr><\/thead><tbody><tr><td><code>\/etc\/opendkim.conf<\/code><\/td><td>Main configuration<\/td><\/tr><tr><td><code>\/etc\/opendkim\/KeyTable<\/code><\/td><td>Signing keys list<\/td><\/tr><tr><td><code>\/etc\/opendkim\/SigningTable<\/code><\/td><td>Allowed signing domains<\/td><\/tr><tr><td><code>\/etc\/opendkim\/TrustedHosts<\/code><\/td><td>Trusted servers<\/td><\/tr><\/tbody><\/table><\/div><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Edit OpenDKIM Configuration<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>vi \/etc\/opendkim.conf<\/code><\/pre>\n\n\n\n<p>Add or update:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>PidFile \/var\/run\/opendkim\/opendkim.pid<br>Mode sv<br>Canonicalization relaxed\/simple<br>Syslog yes<br>SyslogSuccess yes<br>LogWhy yes<br>UserID opendkim:opendkim<br>Socket inet:8891@localhost<br>Umask 002<br>Selector default<br>KeyTable refile:\/etc\/opendkim\/KeyTable<br>SigningTable refile:\/etc\/opendkim\/SigningTable<br>ExternalIgnoreList refile:\/etc\/opendkim\/TrustedHosts<br>InternalHosts refile:\/etc\/opendkim\/TrustedHosts<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Step 6: Generate DKIM Keys<\/h2>\n\n\n\n<p>Create key directories and generate keys.<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>cd \/etc\/opendkim\/keys<br>mkdir yourdomainname.com<br>cd yourdomainname.comopendkim-genkey -d yourdomainname.com -s default<\/code><\/pre>\n\n\n\n<p>Set proper ownership:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>chown opendkim:opendkim ..\/yourdomainname.com -R<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Step 7: Configure KeyTable<\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>vi \/etc\/opendkim\/KeyTable<\/code><\/pre>\n\n\n\n<p>Add:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>default._domainkey.yourdomainname.com yourdomainname.com:default:\/etc\/opendkim\/keys\/yourdomainname.com\/default.private<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Step 8: Configure SigningTable<\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>vi \/etc\/opendkim\/SigningTable<\/code><\/pre>\n\n\n\n<p>Add:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>*@yourdomainname.com default._domainkey.yourdomainkey.yourdomainname.com<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Step 9: Configure Trusted Hosts<\/h2>\n\n\n\n<div class=\"wp-block-group\"><div class=\"wp-block-group__inner-container is-layout-constrained wp-block-group-is-layout-constrained\">\n<pre class=\"wp-block-code\"><code>vi \/etc\/opendkim\/TrustedHosts<\/code><\/pre>\n<\/div><\/div>\n\n\n\n<p>Add:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>127.0.0.1<br>localhost<br>server.yourdomainname.com<br>yourdomainname.com<\/code><\/pre>\n\n\n\n<p>Ensure <strong>localhost<\/strong> is included.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Step 10: Start Services<\/h2>\n\n\n\n<p>Start OpenDKIM first, then Postfix:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/etc\/init.d\/opendkim start<br>\/etc\/init.d\/postfix start<\/code><\/pre>\n\n\n\n<p>Monitor logs:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>tail -f \/var\/log\/maillog<\/code><\/pre>\n\n\n\n<p>You should see OpenDKIM initialization messages.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Step 11: Add DKIM DNS Record<\/h2>\n\n\n\n<p>Retrieve the public DNS key:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>cat \/etc\/opendkim\/keys\/yourdomainname.com\/default.txt<\/code><\/pre>\n\n\n\n<p>Create a <strong>TXT record<\/strong> in DNS:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>default._domainkey IN TXT \"v=DKIM1;k=rsa;p=PUBLIC_KEY\"<\/code><\/pre>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p>Ensure <code>k=rsa<\/code> exists in the record.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading\">Step 12: Configure SPF Record<\/h2>\n\n\n\n<p>Add an SPF record to improve email authentication:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>v=spf1 mx a ip4:SERVER_IP ~all<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Step 13: Test DKIM Setup<\/h2>\n\n\n\n<p>Send a test email:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>echo \"This is a test mail\" | mail -s \"OpenDKIM test mail\" test@gmail.com<\/code><\/pre>\n\n\n\n<p>Check logs:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>tail -f \/var\/log\/maillog<\/code><\/pre>\n\n\n\n<p>Look for:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>DKIM-Signature header added<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Step 14: Verify DKIM Status<\/h2>\n\n\n\n<p>Open the received email headers and confirm:<\/p>\n\n\n\n<pre class=\"wp-block-preformatted\">dkim=pass<\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Conclusion<\/h2>\n\n\n\n<p>Configuring OpenDKIM with Postfix secures outgoing mail using domain authentication. Proper DKIM and SPF setup significantly improves email reputation, prevents spoofing, and ensures reliable inbox delivery.<\/p>\n\n\n\n<p>If you require help, <a href=\"https:\/\/www.supportpro.com\/requestquote.php\">contact SupportPRO Server Admin<\/a><\/p>\n\n\n\n<p class=\"has-text-align-center\"><span id=\"hs-cta-wrapper-9d590242-d641-4383-94b4-8cfd62f0af6b\" class=\"hs-cta-wrapper\"><span id=\"hs-cta-9d590242-d641-4383-94b4-8cfd62f0af6b\" class=\"hs-cta-node hs-cta-9d590242-d641-4383-94b4-8cfd62f0af6b\"><a href=\"https:\/\/www.supportpro.com\/requestquote.php\"><\/a><\/span><\/span><\/p>\n\n\n\n<div class=\"wp-block-media-text alignwide has-media-on-the-right is-stacked-on-mobile is-vertically-aligned-center has-white-background-color has-background\"><div class=\"wp-block-media-text__content\">\n<p class=\"has-large-font-size\">Partner with <strong>SupportPRO<\/strong> for 24\/7 proactive cloud support that keeps your business secure, scalable, and ahead of the curve.<\/p>\n\n\n\n<!--HubSpot Call-to-Action Code --><span class=\"hs-cta-wrapper\" id=\"hs-cta-wrapper-3350a795-db50-482f-9911-301930d1b1be\"><span class=\"hs-cta-node hs-cta-3350a795-db50-482f-9911-301930d1b1be\" id=\"hs-cta-3350a795-db50-482f-9911-301930d1b1be\"><!--[if lte IE 8]><div id=\"hs-cta-ie-element\"><\/div><![endif]--><a href=\"https:\/\/cta-redirect.hubspot.com\/cta\/redirect\/2725694\/3350a795-db50-482f-9911-301930d1b1be\" ><img decoding=\"async\" class=\"hs-cta-img\" id=\"hs-cta-img-3350a795-db50-482f-9911-301930d1b1be\" style=\"border-width:0px;\" src=\"https:\/\/no-cache.hubspot.com\/cta\/default\/2725694\/3350a795-db50-482f-9911-301930d1b1be.png\"  alt=\"Contact Us today!\"\/><\/a><\/span><script charset=\"utf-8\" src=\"https:\/\/js.hscta.net\/cta\/current.js\"><\/script><script type=\"text\/javascript\"> hbspt.cta.load(2725694, '3350a795-db50-482f-9911-301930d1b1be', {\"useNewLoader\":\"true\",\"region\":\"na1\"}); <\/script><\/span><!-- end HubSpot Call-to-Action Code -->\n<\/div><figure class=\"wp-block-media-text__media\"><img fetchpriority=\"high\" decoding=\"async\" width=\"904\" height=\"931\" src=\"https:\/\/www.supportpro.com\/blog\/wp-content\/uploads\/2022\/09\/Free-server-checkup.png\" alt=\"guy server checkup\" class=\"wp-image-12943 size-full\" srcset=\"https:\/\/www.supportpro.com\/blog\/wp-content\/uploads\/2022\/09\/Free-server-checkup.png 904w, https:\/\/www.supportpro.com\/blog\/wp-content\/uploads\/2022\/09\/Free-server-checkup-291x300.png 291w, https:\/\/www.supportpro.com\/blog\/wp-content\/uploads\/2022\/09\/Free-server-checkup-768x791.png 768w, https:\/\/www.supportpro.com\/blog\/wp-content\/uploads\/2022\/09\/Free-server-checkup-585x602.png 585w\" sizes=\"(max-width: 904px) 100vw, 904px\" \/><\/figure><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Email authentication plays a critical role in improving email deliverability and protecting domains from spoofing. DomainKeys Identified Mail (DKIM) adds a digital signature to outgoing emails, allowing receiving servers to&hellip;<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-847","post","type-post","status-publish","format-standard","hentry","category-miscellaneous"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/posts\/847","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/comments?post=847"}],"version-history":[{"count":7,"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/posts\/847\/revisions"}],"predecessor-version":[{"id":16742,"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/posts\/847\/revisions\/16742"}],"wp:attachment":[{"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/media?parent=847"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/categories?post=847"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.supportpro.com\/blog\/wp-json\/wp\/v2\/tags?post=847"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}