{"id":213,"date":"2026-06-02T23:07:18","date_gmt":"2026-06-03T06:07:18","guid":{"rendered":"https:\/\/hostandtech.com\/kb\/whm\/whm-handle-email-delivery-failures-bounces\/"},"modified":"2026-06-02T23:07:18","modified_gmt":"2026-06-03T06:07:18","slug":"whm-handle-email-delivery-failures-bounces","status":"publish","type":"post","link":"https:\/\/hostandtech.com\/kb\/whm\/whm-handle-email-delivery-failures-bounces\/","title":{"rendered":"How to Handle Email Delivery Failures and Bounces in WHM"},"content":{"rendered":"<h2>Overview<\/h2>\n<p>Email delivery failures in WHM are one of the most common support tickets we see. A bounce means the receiving mail server rejected your message and sent back an error. These failures can happen server-wide or affect just one domain, and they almost always leave a clear trail in the logs if you know where to look.<\/p>\n<p>Most WHM servers run Exim as the mail transfer agent (MTA). Understanding how Exim queues, delivers, and reports on mail is the foundation of diagnosing any bounce. Whether you&#8217;re a reseller managing client accounts or a sysadmin on a dedicated server, the troubleshooting process is the same.<\/p>\n<p>This article covers how to read bounce messages, trace delivery through WHM&#8217;s built-in tools and the Exim log, clear stuck queues, and fix the underlying DNS or reputation issues that cause most failures.<\/p>\n<h2>Prerequisites<\/h2>\n<ul>\n<li>WHM root or reseller access (some steps require root)<\/li>\n<li>SSH access for log-level diagnostics (recommended but not mandatory)<\/li>\n<li>Basic familiarity with DNS records (SPF, DKIM, PTR)<\/li>\n<li>cPanel\/WHM version 108 or later (steps are consistent across recent releases)<\/li>\n<li>The bounced email address and approximate send time \u2014 you&#8217;ll need these to search logs efficiently<\/li>\n<\/ul>\n<h2>Step-by-Step Instructions<\/h2>\n<h3>Step 1: Read the Bounce Message First<\/h3>\n<p>Before opening WHM, read the full bounce message that came back to the sender. Most modern mail clients hide the full SMTP response behind a vague subject line, but the original bounce email contains the actual error code and reason.<\/p>\n<p>Look for a 3-digit SMTP code and a description. Here&#8217;s what the first digit tells you:<\/p>\n<ul>\n<li><strong>4xx<\/strong> \u2014 Temporary failure. The receiving server is asking the sender to retry later. Could be a rate limit, greylisting, or a temporary DNS issue.<\/li>\n<li><strong>5xx<\/strong> \u2014 Permanent failure. The receiving server is rejecting the message outright. This needs a fix before retrying.<\/li>\n<\/ul>\n<p>Common 5xx codes you&#8217;ll actually encounter:<\/p>\n<ul>\n<li><strong>550<\/strong> \u2014 User doesn&#8217;t exist, or the sending IP is blacklisted<\/li>\n<li><strong>553<\/strong> \u2014 The sender address failed policy checks (often SPF)<\/li>\n<li><strong>554<\/strong> \u2014 Transaction failed \u2014 catch-all for content filters, spam policies, or reputation blocks<\/li>\n<\/ul>\n<h3>Step 2: Check the Exim Mail Queue in WHM<\/h3>\n<ol>\n<li>Log in to WHM and navigate to <strong>Email &gt; Mail Queue Manager<\/strong>.<\/li>\n<li>You&#8217;ll see a list of queued messages with their delivery status. A message stuck in the queue with repeated retry attempts usually has a 4xx error holding it.<\/li>\n<li>Click on any message ID to see the full delivery log for that message, including the remote server&#8217;s exact response.<\/li>\n<li>To flush the entire queue and force a retry attempt on all deferred messages, click <strong>Run Exim Queue Runner<\/strong> at the top of the page.<\/li>\n<\/ol>\n<p>\ud83d\udcdd Note: Flushing the queue doesn&#8217;t fix the underlying problem. If the receiving server is blocking your IP, retrying will just burn through your retry budget faster. Diagnose first, flush second.<\/p>\n<h3>Step 3: Search the Exim Logs Directly<\/h3>\n<p>WHM&#8217;s UI is useful for a quick look, but the raw Exim log gives you far more detail. The main log lives at <code class=\"\" data-line=\"\">\/var\/log\/exim_mainlog<\/code>.<\/p>\n<p>To find all log entries related to a specific sender or recipient, use <code class=\"\" data-line=\"\">grep<\/code> with the email address:<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-1\"><code class=\"\" data-line=\"\">grep &quot;user@example.com&quot; \/var\/log\/exim_mainlog | tail -50<\/code><\/pre>\n<\/div>\n<p>To find bounces (messages that were rejected), look for lines containing <code class=\"\" data-line=\"\">rejected<\/code> or <code class=\"\" data-line=\"\">R=<\/code> flags:<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-2\"><code class=\"\" data-line=\"\">grep &quot;rejected&quot; \/var\/log\/exim_mainlog | grep &quot;example.com&quot; | tail -30<\/code><\/pre>\n<\/div>\n<p>A typical rejected delivery line looks like this:<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-3\"><code class=\"\" data-line=\"\">2025-11-14 09:22:17 1tKwXm-0003aR-Hg ** recipient@remotedomain.com R=dnslookup T=remote_smtp: SMTP error from remote mail server after RCPT TO: 550 5.7.1 Service unavailable; Client host [198.51.100.45] blocked using Spamhaus SBL<\/code><\/pre>\n<\/div>\n<p>That single line tells you the message ID, the timestamp, the recipient, and the exact rejection reason from the remote server. In this case, the sending IP is on the Spamhaus SBL blacklist.<\/p>\n<h3>Step 4: Check Your Sending IP Reputation<\/h3>\n<p>A blacklisted IP is the most common cause of 550 rejections. On a shared or VPS server, one abusive account can get the entire server&#8217;s IP listed.<\/p>\n<p>Check your main outgoing IP against the major blocklists:<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-4\"><code class=\"\" data-line=\"\">curl -s &quot;https:\/\/api.stopforumspam.org\/api?ip=YOUR.SERVER.IP&amp;json&quot; | python3 -m json.tool<\/code><\/pre>\n<\/div>\n<p>Also check manually at <a href=\"https:\/\/mxtoolbox.com\/blacklists.aspx\" target=\"_blank\" rel=\"noopener\">MXToolbox Blacklist Check<\/a> \u2014 it queries 100+ lists at once and shows which ones flagged you.<\/p>\n<p>If you&#8217;re listed, identify the abusive account first. Remove the listing without fixing the source and you&#8217;ll be relisted within days.<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-5\"><code class=\"\" data-line=\"\"># Find the top sending accounts on your server\n\/usr\/sbin\/exim -bp | grep &quot;^[0-9]&quot; | awk &#039;{print $4}&#039; | sort | uniq -c | sort -rn | head -20<\/code><\/pre>\n<\/div>\n<p>\u26a0 Warning: If you&#8217;re on a shared hosting plan and your IP is being listed due to another tenant&#8217;s activity, contact Host &amp; Tech support \u2014 we can investigate the source and, if necessary, assign a dedicated outbound IP for your account.<\/p>\n<h3>Step 5: Verify SPF, DKIM, and PTR Records<\/h3>\n<p>Even if your IP isn&#8217;t blacklisted, missing or broken DNS records will cause rejections at strict receivers like Google Workspace and Microsoft 365.<\/p>\n<p>Check SPF from the command line:<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-6\"><code class=\"\" data-line=\"\">dig TXT yourdomain.com +short<\/code><\/pre>\n<\/div>\n<p>A valid SPF record looks like this:<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-7\"><code class=\"\" data-line=\"\">&quot;v=spf1 ip4:198.51.100.45 include:_spf.hostandtech.com ~all&quot;<\/code><\/pre>\n<\/div>\n<p>Check DKIM by querying the selector your server uses (default in cPanel is <code class=\"\" data-line=\"\">default._domainkey<\/code>):<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-8\"><code class=\"\" data-line=\"\">dig TXT default._domainkey.yourdomain.com +short<\/code><\/pre>\n<\/div>\n<p>Check the PTR (reverse DNS) record for your server IP:<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-9\"><code class=\"\" data-line=\"\">dig -x YOUR.SERVER.IP +short<\/code><\/pre>\n<\/div>\n<p>The PTR result should resolve back to a hostname that resolves forward to the same IP. Mismatched PTR records are a major red flag for receiving mail servers and will cause silent filtering or outright rejection at some destinations.<\/p>\n<p>\ud83d\udcdd Note: PTR records are set at the IP level, not in your domain&#8217;s DNS zone. On a VPS or dedicated server at Host &amp; Tech, you can set your PTR record through the client portal or by raising a support ticket.<\/p>\n<h3>Step 6: Delete or Bounce Stuck Messages from the Queue<\/h3>\n<p>If you&#8217;ve identified spam or malformed messages clogging the queue, remove them. Don&#8217;t let a queue of 10,000 stuck messages pile up \u2014 Exim&#8217;s performance degrades significantly above a few thousand queued messages.<\/p>\n<p>To remove all frozen messages (messages Exim has given up retrying):<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-10\"><code class=\"\" data-line=\"\">exiqgrep -z -i | xargs exim -Mrm<\/code><\/pre>\n<\/div>\n<p>To remove all messages from a specific sender address:<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-11\"><code class=\"\" data-line=\"\">exiqgrep -f &quot;abuser@yourdomain.com&quot; -i | xargs exim -Mrm<\/code><\/pre>\n<\/div>\n<p>\u26a0 Warning: <code class=\"\" data-line=\"\">exim -Mrm<\/code> permanently deletes messages. There&#8217;s no undo. If you&#8217;re unsure, use <code class=\"\" data-line=\"\">exim -Mvh MESSAGE_ID<\/code> first to view the message headers before removing.<\/p>\n<h2>Common Issues and Troubleshooting<\/h2>\n<h3>550 5.7.1 \u2014 IP Blocked by Spamhaus or Similar<\/h3>\n<p>Your server&#8217;s outgoing IP is on a real-time blocklist (RBL). The remote server is enforcing that list as a policy. Fix the root cause (compromised account, open relay, spam script) first, then request delisting through the specific blocklist&#8217;s removal form. Most major lists process legitimate removal requests within 24 hours.<\/p>\n<h3>Emails to Gmail or Outlook Silently Disappear<\/h3>\n<p>These providers rarely bounce \u2014 they just silently drop mail they don&#8217;t trust. This is genuinely frustrating because there&#8217;s no bounce to trace. Check your DMARC alignment, make sure DKIM is signing correctly, and verify your sending domain has a DMARC record published. Use Google Postmaster Tools (free) to see your domain&#8217;s reputation score with Gmail directly.<\/p>\n<h3>Mail Queued but Never Delivered \u2014 &#8220;Retry Time Not Reached&#8221;<\/h3>\n<p>Exim uses an exponential backoff for retries. If a message failed once, Exim won&#8217;t retry immediately. You&#8217;ll see <code class=\"\" data-line=\"\">retry time not reached<\/code> in the queue. This is normal behaviour. To force an immediate retry: <code class=\"\" data-line=\"\">exim -qff<\/code> from the command line. The double <code class=\"\" data-line=\"\">f<\/code> forces frozen messages to retry too.<\/p>\n<div class=\"ht-code-snippet\"><button class=\"ht-code-snippet__copy\" type=\"button\" aria-label=\"Copy code\"><\/button><span class=\"ht-code-snippet__feedback\">Copied to clipboard<\/span><\/p>\n<pre class=\"ht-code-snippet__code\" id=\"code-block-12\"><code class=\"\" data-line=\"\">exim -qff<\/code><\/pre>\n<\/div>\n<h3>Sender Address Rejected \u2014 &#8220;Relay Not Permitted&#8221;<\/h3>\n<p>This usually means the mail client is trying to send through your server without authenticating, or it&#8217;s using a sender domain that isn&#8217;t hosted on that server. In WHM, check <strong>Exim Configuration Manager &gt; Basic Editor<\/strong> and confirm that SMTP AUTH is enabled. Also verify the account&#8217;s SMTP credentials are correct in the mail client.<\/p>\n<h3>Large Attachments Bouncing with 552 or 554<\/h3>\n<p>The receiving server has a size limit and your message exceeded it. The bounce will include something like <code class=\"\" data-line=\"\">552 5.3.4 Message size exceeds fixed maximum<\/code>. This is a policy decision on the receiver&#8217;s end \u2014 you can&#8217;t override it. Ask the recipient to use a file sharing service instead, or check if your Exim message size limit is set too low for your own users in <strong>WHM &gt; Exim Configuration Manager &gt; Message Size Limit<\/strong>.<\/p>\n<h2>Additional Resources<\/h2>\n<p>If you&#8217;re managing email for multiple clients, a <a href=\"https:\/\/www.hostandtech.com\/reseller-hosting\/\">Reseller Hosting<\/a> plan gives you WHM access to manage Exim settings, DNS zones, and email accounts across all your clients from one interface \u2014 without needing a full dedicated server.<\/p>\n<div class=\"ht-faq-section\">\n<h2>Frequently Asked Questions<\/h2>\n<div class=\"ht-faq-item\">\n<h3 class=\"ht-faq-question\">How do I find why an email bounced in WHM?<\/h3>\n<div class=\"ht-faq-answer\">\n<p>Go to WHM &gt; Email &gt; Mail Queue Manager and click the message ID for full delivery details. For more detail, SSH into the server and search \/var\/log\/exim_mainlog using grep with the sender or recipient address. The log line will include the exact SMTP rejection code and reason from the remote server.<\/p>\n<\/div>\n<\/div>\n<div class=\"ht-faq-item\">\n<h3 class=\"ht-faq-question\">Why are emails from my server going to spam instead of bouncing?<\/h3>\n<div class=\"ht-faq-answer\">\n<p>Large providers like Gmail and Outlook rarely bounce \u2014 they silently filter. This usually means your SPF, DKIM, or DMARC records are missing or misaligned, or your sending IP has a poor reputation score. Register with Google Postmaster Tools to get direct feedback on how Gmail views your domain.<\/p>\n<\/div>\n<\/div>\n<div class=\"ht-faq-item\">\n<h3 class=\"ht-faq-question\">How do I clear the Exim mail queue in WHM?<\/h3>\n<div class=\"ht-faq-answer\">\n<p>In WHM, go to Email &gt; Mail Queue Manager and click Run Exim Queue Runner to retry deferred messages. To remove frozen messages via SSH, run: exiqgrep -z -i | xargs exim -Mrm. Be careful \u2014 this permanently deletes the queued messages.<\/p>\n<\/div>\n<\/div>\n<div class=\"ht-faq-item\">\n<h3 class=\"ht-faq-question\">Can a blacklisted IP affect all domains on a shared server?<\/h3>\n<div class=\"ht-faq-answer\">\n<p>Yes. On shared hosting, all accounts typically share the same outgoing IP. If one account sends spam and gets the IP blacklisted, every domain on that server is affected. If this happens to you on a Host &amp; Tech server, contact support \u2014 we can identify the abusive account and discuss options like a dedicated outbound IP.<\/p>\n<\/div>\n<\/div>\n<div class=\"ht-faq-item\">\n<h3 class=\"ht-faq-question\">What&#039;s the difference between a 4xx and 5xx bounce in email?<\/h3>\n<div class=\"ht-faq-answer\">\n<p>A 4xx code is a temporary rejection \u2014 the remote server is saying &#8216;try again later.&#8217; Exim will keep retrying automatically. A 5xx code is a permanent rejection \u2014 the remote server won&#8217;t accept the message under current conditions. You need to fix the underlying problem (blacklist, bad DNS record, invalid recipient) before it will deliver.<\/p>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Email bounces and delivery failures in WHM usually come down to a handful of repeatable causes \u2014 bad DNS records, a blocked IP, or a misconfigured Exim. This guide walks you through diagnosing and fixing them step by step.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[88],"tags":[563,567,565,564,566,568,89,569],"class_list":["post-213","post","type-post","status-publish","format-standard","hentry","category-whm","tag-email-bounces","tag-email-queue","tag-exim","tag-mail-delivery","tag-smtp-errors","tag-spf-dkim","tag-whm","tag-whm-email-delivery-failures"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.6 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>How to Handle Email Delivery Failures and Bounces in WHM<\/title>\n<meta name=\"description\" content=\"Learn how to diagnose and fix email delivery failures and bounces in WHM. 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