{"id":2253,"date":"2025-03-26T14:26:55","date_gmt":"2025-03-26T14:26:55","guid":{"rendered":"http:\/\/castelis-dev.local\/insights-ressources\/avoid-false-positives-dmarc\/"},"modified":"2025-03-26T14:26:55","modified_gmt":"2025-03-26T14:26:55","slug":"avoid-false-positives-dmarc","status":"publish","type":"article","link":"https:\/\/www.castelis.com\/en\/insights-ressources\/avoid-false-positives-dmarc\/","title":{"rendered":"Avoiding False Positives with DMARC: SPF\/DKIM Practical Guide"},"content":{"rendered":"<p><strong>Avoid False Positives with DMARC<\/strong> is essential to ensure that your legitimate emails are not rejected or classified as spam. DMARC (Domain-based Message Authentication, Reporting &amp; Conformance) is a protocol designed to combat identity theft and phishing, but poor configuration can lead to inadvertent blockages.<\/p>\n<p>In this article, we will explore why some legitimate emails fail with DMARC and <a href=\"https:\/\/www.castelis.com\/dmarc-bien-configurer-bien-proteger-domaines\/\">how to configure SPF and DKIM to avoid conflicts<\/a>, while optimizing <a href=\"https:\/\/www.castelis.com\/en\/?p=11606\">the deliverability of your messages<\/a>.<\/p>\n<p>&nbsp;<\/p>\n<h2>Why Do Some Legitimate Emails Fail with DMARC?<\/h2>\n<h3>Identifying Common Errors that Generate False Positives<\/h3>\n<p>Many DMARC failures are due to:<\/p>\n<ul>\n<li>Incorrectly configured SPF records (too many &#8220;include&#8221; mechanisms, exceeding the 10 DNS lookup limit).<\/li>\n<li>Missing or incorrect DKIM signatures.<\/li>\n<li>Overly restrictive DMARC policies from the start (directly setting to &#8220;quarantine&#8221; or &#8220;reject&#8221;).<\/li>\n<\/ul>\n<h3>Explanation of Conflicts Between SPF, DKIM, and DMARC<\/h3>\n<p>SPF and DKIM play complementary roles: SPF checks if a mail server is authorized to send emails for a given domain, while DKIM allows messages to be signed electronically. DMARC enforces the strict application of these rules.<\/p>\n<p>When an email fails one of these checks, it may be flagged as suspicious or rejected, even if it is legitimate.<\/p>\n<h3>Impact of Overly Strict DMARC Policies<\/h3>\n<p>Setting an overly strict DMARC policy without prior monitoring can result in unintended blockages. It is recommended to start with &#8220;<strong>p=none<\/strong>&#8221; to collect reports and gradually adjust to &#8220;quarantine&#8221; or &#8220;reject&#8221;.<\/p>\n<p>&nbsp;<\/p>\n<h2>Configuring SPF and DKIM to Minimize Conflicts<\/h2>\n<h3>Configuring SPF<\/h3>\n<ul>\n<li>Set up an appropriate SPF record, limiting excessive inclusions.<\/li>\n<li>Test the validity of the SPF record using tools like MXToolbox.<\/li>\n<li>Check the 10 DNS lookup limit to avoid exceeding it.<\/li>\n<\/ul>\n<p>Example of an effective SPF record:<\/p>\n<p><span style=\"color: #1c8037;\">v=spf1 include:_spf.google.com include:spf.protection.outlook.com -all<\/span><\/p>\n<h3>Configuring DKIM<\/h3>\n<ul>\n<li>Generate a DKIM key pair (public\/private).<\/li>\n<li>Publish the public key in the DNS.<\/li>\n<li>Enable DKIM on the sending server and test the configuration with tools like &#8220;DKIM Validator&#8221;.<\/li>\n<\/ul>\n<p>Example of a correct DKIM record:<\/p>\n<p><span style=\"color: #1c8037;\">txt default._domainkey.example.com<\/span><\/p>\n<p><span style=\"color: #1c8037;\">v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3&#8230;<\/span><\/p>\n<p>&nbsp;<\/p>\n<h2>Optimizing DMARC Policy to Avoid False Positives<\/h2>\n<h3>Choosing the Right DMARC Policy<\/h3>\n<ul>\n<li><strong>p=none<\/strong>: Observation phase, no action applied.<\/li>\n<li><strong>p=quarantine<\/strong>: Non-compliant emails are placed in spam.<\/li>\n<li><strong>p=reject<\/strong>: Non-compliant emails are blocked.<\/li>\n<\/ul>\n<p>It is recommended to start with <strong>p=none<\/strong> and gradually progress.<\/p>\n<h3>Interpreting DMARC Reports<\/h3>\n<ul>\n<li>Use tools like <a href=\"https:\/\/dmarcadvisor.com\/fr\/\" target=\"_blank\" rel=\"noopener\">DMARC Advisor<\/a> or Postmark to analyze the results.<\/li>\n<li>Identify legitimate and non-legitimate sending sources.<\/li>\n<li>Adjust SPF and DKIM configurations accordingly.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<h2>Conclusion and Best Practices for Properly Configuring DMARC<\/h2>\n<ul>\n<li>Always test SPF, DKIM, and DMARC changes before deploying them to production.<\/li>\n<li>Monitor DMARC reports for several weeks before applying a strict policy.<\/li>\n<li><a href=\"https:\/\/www.castelis.com\/en\/actualites\/cybersecurite\/set-up-dmarc-enterprise-dmarc-advisor\/\">Raise awareness with IT and marketing teams<\/a> about the importance of email authentication.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p><strong>? Need help understanding where your false positives are coming from and adjusting your DMARC configurations? Let us know ?<\/strong><br \/>\n\n\t\t\t\t\t\t<script>\n\t\t\t\t\t\t\twindow.hsFormsOnReady = window.hsFormsOnReady || [];\n\t\t\t\t\t\t\twindow.hsFormsOnReady.push(()=>{\n\t\t\t\t\t\t\t\thbspt.forms.create({\n\t\t\t\t\t\t\t\t\tportalId: 9318812,\n\t\t\t\t\t\t\t\t\tformId: \"2821dee8-59fb-4bd6-a2c5-10784b9ae3db\",\n\t\t\t\t\t\t\t\t\ttarget: \"#hbspt-form-1777409382000-5378582168\",\n\t\t\t\t\t\t\t\t\tregion: \"na1\",\n\t\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t})});\n\t\t\t\t\t\t<\/script>\n\t\t\t\t\t\t<div class=\"hbspt-form\" id=\"hbspt-form-1777409382000-5378582168\"><\/div><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Experiencing false positives with DMARC? Learn how to configure SPF and DKIM to avoid conflicts and improve your email deliverability.<\/p>\n","protected":false},"author":2,"featured_media":2042,"template":"","meta":{"_acf_changed":false,"content-type":"","footnotes":""},"categories":[75],"tags":[],"class_list":["post-2253","article","type-article","status-publish","has-post-thumbnail","hentry","category-cybersecurite"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/article\/2253","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/article"}],"about":[{"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/types\/article"}],"author":[{"embeddable":true,"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/users\/2"}],"version-history":[{"count":0,"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/article\/2253\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/media\/2042"}],"wp:attachment":[{"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/media?parent=2253"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/categories?post=2253"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.castelis.com\/en\/wp-json\/wp\/v2\/tags?post=2253"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}