{"id":34529,"date":"2026-03-12T12:31:25","date_gmt":"2026-03-12T12:31:25","guid":{"rendered":"https:\/\/1grid.co.za\/knowledge\/?post_type=ht_kb&#038;p=34529"},"modified":"2026-03-16T13:10:54","modified_gmt":"2026-03-16T13:10:54","slug":"smtp-error-550-message-rejected-by-server","status":"publish","type":"ht_kb","link":"https:\/\/1grid.co.za\/knowledge\/smtp-error-550-message-rejected-by-server-how-to-fix-it\/","title":{"rendered":"SMTP Error 550: Message Rejected by Server (How to Fix It)"},"content":{"rendered":"\n<p>If&nbsp;you\u2019ve&nbsp;seen&nbsp;<strong>SMTP Error 550: Message Rejected by Server<\/strong>, your email was blocked by the receiving mail server.&nbsp;That\u2019s&nbsp;frustrating, but it&nbsp;doesn\u2019t&nbsp;mean something is permanently \u201cbroken\u201d.&nbsp;<\/p>\n\n\n\n<p><strong>This guide will help you:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-understand-what-smtp-550-means\">Understand what SMTP 550 means&nbsp;<\/li>\n\n\n\n<li id=\"htoc-identify-the-most-common-causes\">Identify&nbsp;the most common causes&nbsp;<\/li>\n\n\n\n<li id=\"htoc-apply-the-correct-fix-with-confidence\">Apply the correct fix with confidence&nbsp;<\/li>\n\n\n\n<li id=\"htoc-know-when-the-issue-is-outside-your-control\">Know when the issue is outside your control&nbsp;<\/li>\n\n\n\n<li id=\"htoc-prevent-future-occurrences\">Prevent future occurrences&nbsp;<\/li>\n<\/ul>\n\n\n\n<p>You\u2019ll&nbsp;be able to resolve this error&nbsp;<strong>without contacting support<\/strong>&nbsp;in most cases,&nbsp;even if&nbsp;you\u2019re&nbsp;not technical.&nbsp;<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1600\" height=\"600\" src=\"https:\/\/1grid.co.za\/knowledge\/wp-content\/uploads\/2026\/03\/1-grid-Images-for-KB-Articles-1000-x-600-px-6.png\" alt=\"SMTP Error 550: Message Rejected by Server\" class=\"wp-image-34530\"\/><\/figure>\n<\/div>\n\n\n<div class=\"wp-block-ht-block-toc is-style-rounded htoc htoc--position-wide toc-list-style-plain\" data-htoc-state=\"expanded\"><span class=\"htoc__title\"><span class=\"ht_toc_title\">Table of Contents<\/span><span class=\"htoc__toggle\"><svg xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"16\" height=\"16\"><g fill=\"#444\"><path d=\"M15 7H1c-.6 0-1 .4-1 1s.4 1 1 1h14c.6 0 1-.4 1-1s-.4-1-1-1z\"><\/path><path d=\"M15 1H1c-.6 0-1 .4-1 1s.4 1 1 1h14c.6 0 1-.4 1-1s-.4-1-1-1zM15 13H1c-.6 0-1 .4-1 1s.4 1 1 1h14c.6 0 1-.4 1-1s-.4-1-1-1z\"><\/path><\/g><\/svg><\/span><\/span><div class=\"htoc__itemswrap\"><ul class=\"ht_toc_list\"><li class=\"\"><a href=\"#htoc-what-smtp-error-550-actually-means\">What SMTP Error 550 Actually Means&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-why-this-matters\">Why This Matters&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-step-by-step-fix-for-smtp-550-error-mailbox-recipient-rejected\">Step-by-Step Fix for SMTP 550 Error &#8211; Mailbox\/Recipient Rejected&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-quick-fixes-for-common-smtp-550-variations\">Quick&nbsp;Fixes for Common SMTP 550 Variations&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-advanced-optional-fixes-for-technical-users\">Advanced (Optional) Fixes (For Technical Users)&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-before-you-move-on\">Before You Move On&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-if-this-didn-t-work\">If This&nbsp;Didn\u2019t&nbsp;Work&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-common-mistakes-to-avoid\">Common Mistakes to Avoid&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-empowering-insight\">Empowering Insight&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-faqs\">FAQs&nbsp;<\/a><\/li><li class=\"\"><a href=\"#htoc-additional-resources\">Additional&nbsp;Resources&nbsp;<\/a><\/li><\/ul><\/div><\/div>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-what-smtp-error-550-actually-means\"><strong>What SMTP Error 550 Actually Means<\/strong>&nbsp;<\/h2>\n\n\n\n<p><strong>SMTP (Simple Mail Transfer Protocol)<\/strong>&nbsp;is how email moves from your device to your recipient.&nbsp;<br>&nbsp;<br>When you see&nbsp;<strong>550<\/strong>, the receiving server has rejected your message.&nbsp;<\/p>\n\n\n\n<p>In simple terms,&nbsp;<strong>the mail server said,&nbsp;<em>\u201cNo, I won\u2019t accept this.\u201d<\/em><\/strong>&nbsp;<\/p>\n\n\n\n<p>This can happen for many reasons, from typos in the address to authentication issues to spam filtering.&nbsp;<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-why-this-matters\"><strong>Why This Matters<\/strong>&nbsp;<\/h2>\n\n\n\n<p>If ignored, repeated 550 errors can:&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-delay-important-communication\">Delay important communication&nbsp;<\/li>\n\n\n\n<li id=\"htoc-hurt-your-domain-s-email-deliverability\">Hurt your domain\u2019s email deliverability&nbsp;<\/li>\n\n\n\n<li id=\"htoc-trigger-more-errors-or-blacklist-flags\">Trigger more errors or blacklist flags&nbsp;<\/li>\n<\/ul>\n\n\n\n<p>Understanding the \u201cwhy\u201d helps you fix the right thing confidently.&nbsp;<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-step-by-step-fix-for-smtp-550-error-mailbox-recipient-rejected\"><strong>Step-by-Step Fix for SMTP 550 Error &#8211; Mailbox\/Recipient Rejected<\/strong>&nbsp;<\/h2>\n\n\n\n<p>Follow these steps in order.&nbsp;<\/p>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>1: Confirm the Full Error Message&nbsp;<\/strong><\/summary>\n<p id=\"htoc-1-confirm-the-full-error-message\">Open the bounce message or email error details.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-ensure-it-specifically-references-variations-of\">Ensure it specifically references variations of:&nbsp;<\/p>\n\n\n\n<pre id=\"htoc-550-requested-action-not-taken\" class=\"wp-block-code\"><code>550 Requested&nbsp;action&nbsp;not taken&nbsp;\n550 No such user here&nbsp;\n550 Mailbox unavailable&nbsp;\n550 Relay access denied&nbsp;\n550 5.1.1 User unknown&nbsp;<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li><\/li>\n<\/ul>\n\n\n\n<ul class=\"wp-block-list\">\n<li><\/li>\n<\/ul>\n\n\n\n<ul class=\"wp-block-list\">\n<li><\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-1-confirm-the-full-error-message1\">If the error shows 552, 554, 535, or 421, refer to our SMTP&nbsp;Error Codes<a href=\"https:\/\/1grid.co.za\/knowledge\/a-guide-to-smtperror-codes\/\" target=\"_blank\" rel=\"noreferrer noopener\"> <strong>guide<\/strong><\/a> for more information.&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>2: Verify the Recipient Email Address&nbsp;<\/strong><\/summary>\n<p id=\"htoc-step-2-verify-the-recipient-email-address\">SMTP 550 often means the mailbox does not exist.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-check-for\">Check for:&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-spelling-errors\">Spelling errors&nbsp;<\/li>\n\n\n\n<li id=\"htoc-incorrect-domain-name\">Incorrect domain name&nbsp;<\/li>\n\n\n\n<li id=\"htoc-extra-spaces\">Extra spaces&nbsp;<\/li>\n\n\n\n<li id=\"htoc-old-or-deactivated-addresses\">Old or deactivated addresses&nbsp;<\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-example\">Example:&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-correct-name-domain-co-za\">Correct:&nbsp;<a href=\"mailto:name@domain.co.za\" target=\"_blank\" rel=\"noreferrer noopener\">name@domain.co.za<\/a>&nbsp;<\/li>\n\n\n\n<li id=\"htoc-incorrect-name-domain-co-za\">Incorrect:&nbsp;<a href=\"mailto:name@domain,co.za\" target=\"_blank\" rel=\"noreferrer noopener\">name@domain,co.za<\/a>&nbsp;<\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-step-2-verify-the-recipient-email-address1\">If&nbsp;sending to&nbsp;a mailing list, remove invalid addresses.&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>3: Confirm the Recipient Domain is Active&nbsp;<\/strong><\/summary>\n<p id=\"htoc-step-3-confirm-the-recipient-domain-is-active\">If the address is correct:&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-check-that-the-domain-exists\">Check that the domain exists&nbsp;<\/li>\n\n\n\n<li id=\"htoc-ensure-it-has-valid-mx-records\">Ensure it has valid<strong> <a href=\"https:\/\/1grid.co.za\/knowledge\/?s=MX&amp;ht-kb-search=1&amp;lang=\">MX records<\/a>&nbsp;<\/strong><\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-step-3-confirm-the-recipient-domain-is-active1\">If the domain recently changed hosting, allow<strong> <a href=\"https:\/\/1grid.co.za\/knowledge\/what-is-dns-propagation-and-why-does-it-take-so-long\/\">DNS propagation time<\/a><\/strong>.&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>4: Check SMTP Authentication (If Sending Fails Immediately)&nbsp;<\/strong><\/summary>\n<p id=\"htoc-step-4-check-smtp-authentication-if-sending-fails-immediately\">If you see:&nbsp;<\/p>\n\n\n\n<pre id=\"htoc-550-relay-denied-550-authentication-required\" class=\"wp-block-code\"><code>550 Relay denied&nbsp;<br>550 Authentication&nbsp;required&nbsp;<\/code><\/pre>\n\n\n\n<p id=\"htoc-verify\">Verify:&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-smtp-authentication-is-enabled\"><a href=\"https:\/\/1grid.co.za\/knowledge\/recommended-server-settings-for-email-encryption-ports\/#htoc-which-smtp-port-should-i-choose\"><strong>SMTP<\/strong><\/a> authentication is enabled&nbsp;<\/li>\n\n\n\n<li id=\"htoc-you-are-using-your-full-email-address-as-username\">You are using your full email address as the username&nbsp;<\/li>\n\n\n\n<li id=\"htoc-the-password-is-correct\">The password is correct&nbsp;<\/li>\n\n\n\n<li>Port 465 (SSL) or 587 (TLS) is used&nbsp;<\/li>\n<\/ul>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>5:&nbsp;Review Delivery Logs (Basic&nbsp;Level)&nbsp;<\/strong><\/summary>\n<p id=\"htoc-step-5-review-delivery-logs-basic-level\">Log in to:&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-cpanel-email-track-delivery\"><strong><a href=\"https:\/\/1grid.co.za\/knowledge\/how-to-log-in-to-cpanel-via-your-1-grid-customer-zone\/\">cPanel<\/a> <\/strong>\u2192 Email \u2192 Track Delivery&nbsp;<\/li>\n\n\n\n<li id=\"htoc-plesk-websites-amp-domains-select-your-domain-mail-track-email-delivery\"><strong><a href=\"https:\/\/1grid.co.za\/knowledge\/plesk-how-do-i-login-via-customer-zone\/\">Plesk<\/a> <\/strong>\u2192 Websites &amp; Domains \u2192 Select your domain \u2192 Mail \u2192 Track Email Delivery&nbsp;<\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-confirm-whether-the-message-was\">Confirm whether the message was:&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-rejected-permanently-550\">Rejected permanently (550)&nbsp;<\/li>\n\n\n\n<li id=\"htoc-or-deferred-temporary-issue\">Or deferred (temporary issue)&nbsp;<\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-step-5-review-delivery-logs-basic-level1\">A 550 error is typically a permanent rejection.&nbsp;<\/p>\n<\/details>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-quick-fixes-for-common-smtp-550-variations\"><strong>Quick&nbsp;Fixes for Common SMTP 550 Variations<\/strong>&nbsp;<\/h2>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>1. 550 Requested&nbsp;Action&nbsp;Not&nbsp;Taken:&nbsp;Mailbox&nbsp;Unavailable&nbsp;<\/strong><\/summary>\n<p id=\"htoc-1-550-requested-action-not-taken-mailbox-unavailable\"><strong>What It Means:<\/strong>&nbsp;<br>The recipient\u2019s mailbox&nbsp;doesn\u2019t&nbsp;exist or&nbsp;can\u2019t&nbsp;receive mail.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-double-check-the-email-address-spelling\">Double\u2011check the email address spelling&nbsp;<\/li>\n\n\n\n<li id=\"htoc-confirm-with-the-recipient\">Confirm with the recipient&nbsp;<\/li>\n\n\n\n<li id=\"htoc-try-again-later\">Try again later&nbsp;<\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-1-550-requested-action-not-taken-mailbox-unavailable1\"><strong>Why It Happens:&nbsp;<\/strong>Often&nbsp;simple typos or inactive accounts.&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>2. 550 5.1.1 Email&nbsp;Account&nbsp;Does&nbsp;Not&nbsp;Exist&nbsp;<\/strong><\/summary>\n<p id=\"htoc-2-550-5-1-1-email-account-does-not-exist\"><strong>What It Means:<\/strong>&nbsp;<br>The recipient address is invalid.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it1\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-correct-any-typos-or-spelling-errors\">Correct any&nbsp;typos or&nbsp;spelling errors&nbsp;<\/li>\n\n\n\n<li id=\"htoc-confirm-the-address-with-the-recipient\">Confirm the address with the recipient&nbsp;<\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-2-550-5-1-1-email-account-does-not-exist1\">Request an alternative email address if needed&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>3. 550 5.7.1 Unable to&nbsp;Relay&nbsp;<\/strong><\/summary>\n<p id=\"htoc-3-550-5-7-1-unable-to-relay\"><strong>What It Means:<\/strong>&nbsp;<br>Your mail server&nbsp;isn\u2019t&nbsp;authorised to send to this destination.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it11\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-confirm-your-outgoing-smtp-server-settings-host-port-ssl-tls\">Confirm your&nbsp;<strong><a href=\"https:\/\/1grid.co.za\/knowledge\/recommended-server-settings-for-email-encryption-ports\/#htoc-recommended-secure-email-settings\">outgoing (SMTP) server settings<\/a>&nbsp;<\/strong>(host, port, SSL\/TLS)&nbsp;<\/li>\n\n\n\n<li id=\"htoc-ensure-smtp-authentication-is-enabled-in-your-mail-client\">Ensure&nbsp;SMTP&nbsp;authentication&nbsp;is enabled in your mail client&nbsp;<\/li>\n<\/ul>\n\n\n\n<p id=\"htoc-3-550-5-7-1-unable-to-relay1\"><strong>Before You Move On:<\/strong>&nbsp;Check for public\/unsecured&nbsp;networks, as&nbsp;they often block mail submission.&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>4. 550 5.4.5 Daily&nbsp;Sending&nbsp;Quota&nbsp;Exceeded&nbsp;<\/strong><\/summary>\n<p id=\"htoc-4-550-5-4-5-daily-sending-quota-exceeded\"><strong>What It Means:&nbsp;<\/strong>&nbsp;<br>You hit a sending limit.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it111\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-slow-down-email-rate\">Slow down the email rate&nbsp;<\/li>\n\n\n\n<li>Use a dedicated email marketing service for bulk emails.&nbsp;<\/li>\n<\/ul>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>5. 550 5.2.1 Mailbox&nbsp;Cannot&nbsp;Receive&nbsp;Email&nbsp;<\/strong><\/summary>\n<p id=\"htoc-5-550-5-2-1-mailbox-cannot-receive-email\"><strong>What It Means:&nbsp;<\/strong>&nbsp;<br>The recipient\u2019s mailbox is full or restricted.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it1111\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-ask-the-recipient-to-clear-space-or-adjust-mailbox-settings\">Ask the recipient to clear space or adjust mailbox settings&nbsp;<\/li>\n\n\n\n<li>Request an alternative contact address&nbsp;<\/li>\n<\/ul>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>6. 550 5.7.1&nbsp;Message Rejected Due to Content or Spam Filters&nbsp;<\/strong><\/summary>\n<p id=\"htoc-6-550-5-7-1-message-rejected-due-to-content-or-spam-filters\"><strong>What It Means:&nbsp;<\/strong>&nbsp;<br>Filters flagged your email.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it11111\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-remove-suspicious-links-or-attachments\">Remove<strong> <a href=\"https:\/\/1grid.co.za\/knowledge\/email-security-avoid-being-labeled-as-a-spammer\/\">suspicious links <\/a><\/strong>or attachments&nbsp;<\/li>\n\n\n\n<li id=\"htoc-avoid-trigger-phrases-or-heavy-formatting\">Avoid <strong><a href=\"https:\/\/1grid.co.za\/knowledge\/email-security-avoid-being-labeled-as-a-spammer\/\">trigger phrases<\/a> <\/strong>or <a href=\"https:\/\/1grid.co.za\/knowledge\/email-security-avoid-being-labeled-as-a-spammer\/\"><strong>heavy formatting&nbsp;<\/strong><\/a><\/li>\n\n\n\n<li>Ask the recipient to<strong> <a href=\"https:\/\/www.techtarget.com\/whatis\/definition\/whitelist\">whitelist<\/a> <\/strong>your address&nbsp;<\/li>\n<\/ul>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>7. 550 5.1.10 Recipient&nbsp;Not in&nbsp;Directory&nbsp;<\/strong><\/summary>\n<p id=\"htoc-7-550-5-1-10-recipient-not-in-directory\"><strong>What It Means:<\/strong>&nbsp;<br>Recipient&nbsp;isn\u2019t&nbsp;recognised&nbsp;on the mail system.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it111111\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-verify-the-email-address\">Verify the email address&nbsp;<\/li>\n\n\n\n<li>Ask the recipient to confirm&nbsp;the domain and&nbsp;directory settings&nbsp;<\/li>\n<\/ul>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>8. 550 5.7.1 Message&nbsp;Size&nbsp;Exceeds&nbsp;Limit&nbsp;<\/strong><\/summary>\n<p id=\"htoc-8-550-5-7-1-message-size-exceeds-limit\"><strong>What It Means:<\/strong>&nbsp;<br>Your email or attachment is too large.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it1111111\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-compress-attachments\"><a href=\"https:\/\/compresto.app\/blog\/reduce-file-size-for-email-attachments\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Compress attachments<\/strong><\/a>&nbsp;<\/li>\n\n\n\n<li>Use&nbsp;<a href=\"https:\/\/www.pcmag.com\/picks\/the-best-cloud-storage-and-file-sharing-services\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>cloud file-sharing services<\/strong><\/a>&nbsp;<\/li>\n<\/ul>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>9. 550 Message&nbsp;Headers&nbsp;Fail&nbsp;Syntax&nbsp;Check&nbsp;<\/strong><\/summary>\n<p id=\"htoc-9-550-message-headers-fail-syntax-check\"><strong>What It Means:<\/strong>&nbsp;<br>The email headers are incorrectly formatted.&nbsp;<\/p>\n\n\n\n<p id=\"htoc-how-to-fix-it11111111\"><strong>How to Fix It:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-manually-re-enter-the-recipient-s-email-address\">Manually&nbsp;re-enter&nbsp;the recipient\u2019s email&nbsp;address&nbsp;<\/li>\n\n\n\n<li id=\"htoc-check-from-to-and-subject-fields\">Check \u201cFrom\u201d,&nbsp;\u201cTo\u201d,&nbsp;and \u201cSubject\u201d fields&nbsp;<\/li>\n\n\n\n<li>Disable problematic mail client plugins&nbsp;<\/li>\n<\/ul>\n<\/details>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-advanced-optional-fixes-for-technical-users\"><strong>Advanced (Optional) Fixes (For Technical Users)<\/strong>&nbsp;<\/h2>\n\n\n\n<p>Administrators&nbsp;or&nbsp;Technical Users can diagnose permanent rejections and resolve server-level issues.&nbsp;<\/p>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>1. Check Mail Logs&nbsp;<\/strong><\/summary>\n<p id=\"htoc-1-check-mail-logs\"><strong>Exim<\/strong>&nbsp;<\/p>\n\n\n\n<pre id=\"htoc-grep-550-var-log-exim-mainlog-tail-f-var-log-exim-mainlog\" class=\"wp-block-code\"><code>grep \"550\" \/var\/log\/exim_mainlog&nbsp;<br>tail -f \/var\/log\/exim_mainlog&nbsp;<\/code><\/pre>\n\n\n\n<p id=\"htoc-postfix\"><strong>Postfix<\/strong>&nbsp;<\/p>\n\n\n\n<pre id=\"htoc-grep-550-var-log-maillog-tail-f-var-log-maillog\" class=\"wp-block-code\"><code>grep \"550\" \/var\/log\/mail.log\ntail -f \/var\/log\/mail.log<\/code><\/pre>\n\n\n\n<p id=\"htoc-1-check-mail-logs1\"><strong>Goal:<\/strong>&nbsp;Identify&nbsp;recurring rejections, recipient domains, or specific sender issues.&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>2. Review Mail Queue&nbsp;<\/strong><\/summary>\n<p id=\"htoc-2-review-mail-queue\"><strong>Exim<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>List queued messages:&nbsp;<\/li>\n<\/ul>\n\n\n\n<pre id=\"htoc-exim-bp-list-queued-messages-exim-mrm-lt-message-id-gt-remove-stuck-messages-if-needed\" class=\"wp-block-code\"><code>exim&nbsp;-bp&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Remove stuck messages, if needed:<\/li>\n<\/ul>\n\n\n\n<pre id=\"htoc-1\" class=\"wp-block-code\"><code>exim -Mrm &lt;message-id&gt;<\/code><\/pre>\n\n\n\n<p id=\"htoc-postfix1\"><strong>Postfix<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>List queued messages:<\/li>\n<\/ul>\n\n\n\n<pre id=\"htoc-postqueue-p-postsuper-d-lt-queue-id-gt-delete-stuck-messages\" class=\"wp-block-code\"><code>postqueue&nbsp;-p&nbsp;<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Delete stuck messages:<\/li>\n<\/ul>\n\n\n\n<pre id=\"htoc-11\" class=\"wp-block-code\"><code>postsuper -d &lt;queue-id&gt;<\/code><\/pre>\n\n\n\n<p id=\"htoc-notes\"><strong>Notes:<\/strong>&nbsp;<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-verify-rejected-vs-deferred-messages\">Verify rejected vs. deferred messages&nbsp;<\/li>\n\n\n\n<li>Avoid mass deletion unless confirmed undeliverable&nbsp;<\/li>\n<\/ul>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>3. Confirm Authentication &amp; Policies&nbsp;<\/strong><\/summary>\n<p id=\"htoc-3-confirm-authentication-amp-policies\">Check SMTP authentication logs:&nbsp;<\/p>\n\n\n\n<pre id=\"htoc-3-confirm-authentication-amp-policies1\" class=\"wp-block-code\"><code>\/var\/log\/exim_mainlog&nbsp;or&nbsp;\/var\/log\/maillog&nbsp;<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-ensure-spf-dkim-dmarc-alignment\">Ensure SPF\/DKIM\/DMARC alignment&nbsp;<\/li>\n\n\n\n<li id=\"htoc-run-ip-reputation-checks-to-verify-your-server-is-not-blacklisted\">Run IP reputation checks to verify your server is not blacklisted:&nbsp;\n<ul class=\"wp-block-list\">\n<li>Verify SPF<\/li>\n\n\n\n<li>Verify DKIM<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<pre id=\"htoc-3-confirm-authentication-amp-policies11\" class=\"wp-block-code\"><code>dig +short TXT example.com \n\ndig +short TXT default._domainkey.example.com<\/code><\/pre>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>4. Test Delivery via CLI&nbsp;<\/strong><\/summary>\n<pre id=\"htoc-4-test-delivery-via-cli\" class=\"wp-block-code\"><code>swaks&nbsp;--to&nbsp;<a href=\"mailto:recipient@example.com\" target=\"_blank\" rel=\"noreferrer noopener\">recipient@example.com<\/a>&nbsp;--server mx.example.com --data \"Subject: Test\\n\\nHello\"&nbsp;\n\ntelnet mx.example.com 25&nbsp;<\/code><\/pre>\n\n\n\n<p id=\"htoc-4-test-delivery-via-cli1\"><strong>Goal:<\/strong>&nbsp;Confirm server accepts mail from authenticated user&nbsp;<\/p>\n<\/details>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-before-you-move-on\"><strong>Before You Move On<\/strong>&nbsp;<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-ensure-recipient-addresses-exist\">Ensure recipient addresses exist&nbsp;<\/li>\n\n\n\n<li id=\"htoc-confirm-authentication-is-correct\">Confirm authentication is correct&nbsp;<\/li>\n\n\n\n<li id=\"htoc-verify-dns-mx-records-and-ip-reputation\">Verify DNS \/ MX records and IP reputation&nbsp;<\/li>\n\n\n\n<li id=\"htoc-hosting-and-mailboxes-remain-unaffected\">Hosting and mailboxes&nbsp;remain&nbsp;unaffected&nbsp;<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-if-this-didn-t-work\"><strong>If This&nbsp;Didn\u2019t&nbsp;Work<\/strong>&nbsp;<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-try-sending-to-a-different-domain-e-g-gmail\">Try sending to a different domain (e.g., Gmail)&nbsp;<\/li>\n\n\n\n<li id=\"htoc-check-your-domain-isn-t-blacklisted\">Check that your domain&nbsp;isn\u2019t&nbsp;<strong><a href=\"https:\/\/1grid.co.za\/knowledge\/how-to-check-if-my-ip-is-blacklisted\/\">blacklisted<\/a>&nbsp;<\/strong><\/li>\n\n\n\n<li id=\"htoc-confirm-spf-dkim-dmarc\">Confirm<strong>&nbsp;<\/strong><a href=\"https:\/\/1grid.co.za\/knowledge\/?s=SPF&amp;ht-kb-search=1&amp;lang=\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>SPF<\/strong><\/a>\/<a href=\"https:\/\/1grid.co.za\/knowledge\/?s=DKIM&amp;ht-kb-search=1&amp;lang=\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>DKIM<\/strong><\/a>\/<a href=\"https:\/\/1grid.co.za\/knowledge\/?s=DMARC&amp;ht-kb-search=1&amp;lang=\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>DMARC<\/strong><\/a>&nbsp;<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-common-mistakes-to-avoid\"><strong>Common Mistakes to Avoid<\/strong>&nbsp;<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li id=\"htoc-guessing-server-settings-always-verify\">Guessing server settings&nbsp;&#8211;&nbsp;always verify&nbsp;<\/li>\n\n\n\n<li id=\"htoc-assuming-it-s-temporary-550-is-permanent-fail-until-fixed\">Assuming&nbsp;it\u2019s&nbsp;temporary&nbsp;&#8211;&nbsp;550 is \u201cpermanent fail\u201d until fixed&nbsp;<\/li>\n\n\n\n<li id=\"htoc-ignoring-authentication-this-often-triggers-spam-rejections\">Ignoring authentication&nbsp;&#8211;&nbsp;this often triggers spam rejections&nbsp;<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-empowering-insight\"><strong>Empowering Insight<\/strong>&nbsp;<\/h2>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1600\" height=\"300\" src=\"https:\/\/1grid.co.za\/knowledge\/wp-content\/uploads\/2026\/03\/1-grid-Images-for-KB-Articles-1000-x-600-px-1600-x-300-px.png\" alt=\"Empowering Insight\" class=\"wp-image-34464\"\/><\/figure>\n<\/div>\n\n\n<p>If the error includes the word&nbsp;<strong>\u201cspam\u201d<\/strong>,&nbsp;it\u2019s&nbsp;usually about&nbsp;<strong>trust<\/strong>, not technology.&nbsp;Fixing SPF\/DKIM,&nbsp;along with&nbsp;clean content,&nbsp;nearly always&nbsp;resolves it.&nbsp;<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-faqs\"><strong>FAQs<\/strong>&nbsp;<\/h2>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>Q. Can SMTP Error 550 be caused by the sender?&nbsp;<\/strong><\/summary>\n<p id=\"htoc-q-can-smtp-error-550-be-caused-by-the-sender-yes-due-to-incorrect-settings-lack-of-authentication-or-reputation-issues\">Yes, due to incorrect settings, lack of authentication, or reputation issues.&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>Q. Is SMTP Error 550 temporary?&nbsp;<\/strong><\/summary>\n<p id=\"htoc-q-is-smtp-error-550-temporary-no-it-requires-action-before-delivery-will-succeed\">No, it requires action before delivery will succeed.&nbsp;<\/p>\n<\/details>\n\n\n\n<details class=\"wp-block-details is-layout-flow wp-block-details-is-layout-flow\"><summary><strong>Q. Can I prevent SMTP Error 550?&nbsp;<\/strong><\/summary>\n<p id=\"htoc-q-can-i-prevent-smtp-error-550-good-email-hygiene-and-authentication-reduce-future-issues\">Good email hygiene and authentication reduce future issues.&nbsp;<\/p>\n<\/details>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-additional-resources\"><strong>Additional&nbsp;Resources<\/strong>&nbsp;<\/h2>\n\n\n\n<p><a href=\"https:\/\/1grid.co.za\/knowledge\/a-guide-to-smtperror-codes\/\"><strong>A Guide to SMTP Error Codes<\/strong><\/a><br><a href=\"https:\/\/1grid.co.za\/knowledge\/what-is-an-spf-record-and-why-it-matters-in-dns-for-email\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>How to Set Up SPF<\/strong><\/a><strong>&nbsp;\/&nbsp;<\/strong><a href=\"https:\/\/1grid.co.za\/knowledge\/?s=DKIM&amp;ht-kb-search=1&amp;lang=\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>DKIM<\/strong><\/a><strong>&nbsp;\/&nbsp;<\/strong><a href=\"https:\/\/1grid.co.za\/knowledge\/?s=DMARC&amp;ht-kb-search=1&amp;lang=\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>DMARC<\/strong><\/a>&nbsp;<br><a href=\"https:\/\/1grid.co.za\/knowledge\/heres-why-emails-go-to-spam\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Why Emails Go to Spam<\/strong><\/a>&nbsp;<br><a href=\"https:\/\/1grid.co.za\/knowledge\/what-is-ip-blacklisting\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Check If Your Domain Is Blacklisted<\/strong><\/a>&nbsp;<br><a href=\"https:\/\/1grid.co.za\/knowledge\/mailchannels-errors-codes\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Common Mailserver Errors Explained<\/strong><\/a><strong>&nbsp;<\/strong>&nbsp;<br><a href=\"https:\/\/1grid.co.za\/knowledge\/email-restrictions\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Email Sending Limits<\/strong><\/a>&nbsp;<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"htoc-need-additional-support\"><strong>Need Additional Support?<\/strong>&nbsp;<\/h2>\n\n\n\n<p><strong>We&#8217;re&nbsp;Here to&nbsp;<\/strong><a href=\"https:\/\/1grid.co.za\/knowledge\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Help<\/strong><\/a><strong>:<\/strong>&nbsp;<\/p>\n\n\n\n<p>Understanding SMTP Error 550 and how to fix this&nbsp;doesn\u2019t&nbsp;have&nbsp;to&nbsp;feel technical&nbsp;with&nbsp;this&nbsp;easy-to-reference guide. Stuck?&nbsp;Check out our&nbsp;<a href=\"https:\/\/1grid.co.za\/knowledge\/1-grid-scope-of-support\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Scope of Support<\/strong><\/a>, and then contact our Support Team for&nbsp;further&nbsp;clarity and&nbsp;guidance&nbsp;(<a href=\"https:\/\/1grid.co.za\/contact-us\/\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>https:\/\/1grid.co.za\/contact-us\/<\/strong><\/a>).&nbsp;We&#8217;re&nbsp;ready&nbsp;to see&nbsp;how we can help!&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>If&nbsp;you\u2019ve&nbsp;seen&nbsp;SMTP Error 550: Message Rejected by Server, your email was blocked by the receiving mail server.&nbsp;That\u2019s&nbsp;frustrating, but it&nbsp;doesn\u2019t&nbsp;mean something is permanently \u201cbroken\u201d.&nbsp; This guide will help you:&nbsp; You\u2019ll&nbsp;be able to resolve this error&nbsp;without contacting support&nbsp;in most cases,&nbsp;even if&nbsp;you\u2019re&nbsp;not technical.&nbsp; What SMTP Error 550 Actually Means&nbsp; SMTP (Simple Mail Transfer Protocol)&nbsp;is&#8230;<\/p>\n","protected":false},"author":21,"comment_status":"closed","ping_status":"closed","template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"ht-kb-category":[1194],"ht-kb-tag":[1711,1710,1712,1494,1707,1514,1713,1706,1701],"class_list":["post-34529","ht_kb","type-ht_kb","status-publish","format-standard","hentry","ht_kb_category-email-troubleshooting","ht_kb_tag-550-mailbox-rejected","ht_kb_tag-550-message-rejected-by-server","ht_kb_tag-550-recipient-rejected","ht_kb_tag-email-configuration","ht_kb_tag-email-delivery-issues","ht_kb_tag-email-troubleshooting","ht_kb_tag-smtp-550-fix","ht_kb_tag-smtp-bounce-errors","ht_kb_tag-smtp-errors"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v22.0 - 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