{"id":5201,"date":"2026-03-09T01:15:06","date_gmt":"2026-03-09T01:15:06","guid":{"rendered":"https:\/\/emailwarmup.com\/blog\/?p=5201"},"modified":"2026-03-09T01:15:52","modified_gmt":"2026-03-09T01:15:52","slug":"how-to-fix-550-5-7-1-message-blocked-low-domain-reputation","status":"publish","type":"post","link":"https:\/\/emailwarmup.com\/blog\/email-errors\/how-to-fix-550-5-7-1-message-blocked-low-domain-reputation\/","title":{"rendered":"How To Fix 550 5.7.1 | Message Blocked [Low Domain Reputation]"},"content":{"rendered":"\n<figure class=\"wp-block-image size-full\"><img fetchpriority=\"high\" decoding=\"async\" width=\"3406\" height=\"2168\" src=\"https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/550-5.7.1_11zon.jpg\" alt=\"550 5.7.1\" class=\"wp-image-5202\"\/><\/figure>\n\n\n\n<p>The 550 5.7.1 error means the receiving server blocked your message due to low <a href=\"https:\/\/emailwarmup.com\/blog\/email-deliverability\/sender-reputation\/\">sender reputation<\/a> \u2014 your domain or IP is flagged for spam-like behavior.\u00a0<\/p>\n\n\n\n<p>Fix it by implementing proper <a href=\"https:\/\/emailwarmup.com\/blog\/email-authentication\/spf-record\/\">SPF<\/a>\/<a href=\"https:\/\/emailwarmup.com\/blog\/email-authentication\/dkim\">DKIM<\/a>\/<a href=\"https:\/\/emailwarmup.com\/blog\/email-authentication\/dmarc\">DMARC<\/a> authentication, checking <a href=\"https:\/\/emailwarmup.com\/blog\/email-blacklist\/how-to-check-if-your-email-is-blacklisted\/\">blacklist status<\/a>, reducing volume, and rebuilding trust through gradual <a href=\"https:\/\/emailwarmup.com\/\" target=\"_blank\" rel=\"noreferrer noopener\">email warmup<\/a>.<\/p>\n\n\n\n<p>Unlike addressing errors (5.1.x) or mailbox state errors (5.2.x), the 5.7.1 code signals a <em>trust<\/em> problem.&nbsp;<\/p>\n\n\n\n<p>Providers like Gmail explicitly state they use 5.7.1 for &#8220;likely unsolicited&#8221; mail and &#8220;very low reputation&#8221; of the sending domain or IP. Recovery requires changing sending behavior \u2014 not just fixing a single setting.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Quick skim \u2014 550 5.7.1 error overview<\/h2>\n\n\n\n<p>The 550 5.7.1 error indicates delivery rejection due to sender reputation or policy violations.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td>Attribute<\/td><td>Details<\/td><\/tr><tr><td>Error code<\/td><td>550 5.7.1<\/td><\/tr><tr><td>Category<\/td><td>Reputation\/policy rejection<\/td><\/tr><tr><td>Meaning<\/td><td>Sender not authorized; message appears unsolicited<\/td><\/tr><tr><td>Severity<\/td><td>Permanent (requires behavioral change)<\/td><\/tr><tr><td>Common causes<\/td><td>Low reputation, blacklisting, authentication failure, spam content<\/td><\/tr><tr><td>Fix approach<\/td><td>Fix authentication \u2192 check blacklists \u2192 clean list \u2192 warm gradually<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">What does 550 5.7.1 mean?<\/h2>\n\n\n\n<p>The enhanced code 5.7.1 means &#8220;delivery not authorized, message refused.&#8221; Providers interpret this broadly \u2014 any policy-based rejection where the sender isn&#8217;t trusted enough for delivery.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Provider interpretations<\/h3>\n\n\n\n<p>Gmail provides the most detailed 5.7.1 explanations in their error catalog:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td>Gmail Text<\/td><td>Meaning<\/td><\/tr><tr><td>&#8220;very low reputation of the sending domain&#8221;<\/td><td>Domain reputation tanked<\/td><\/tr><tr><td>&#8220;very low reputation of the sending IP address&#8221;<\/td><td>IP flagged for spam<\/td><\/tr><tr><td>&#8220;likely unsolicited&#8221;<\/td><td>Content\/pattern matches spam<\/td><\/tr><tr><td>&#8220;RFC 5322 violation&#8221;<\/td><td>Message structure non-compliant<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>Microsoft 365 uses 5.7.1 for various policy blocks:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td>Microsoft Text<\/td><td>Meaning<\/td><\/tr><tr><td>&#8220;Service unavailable, sending domain blocked&#8221;<\/td><td>Domain blacklisted<\/td><\/tr><tr><td>&#8220;Access denied, spam filter blocks&#8221;<\/td><td>Content\/reputation filter triggered<\/td><\/tr><tr><td>&#8220;External senders are not permitted&#8221;<\/td><td>Recipient restricts external mail<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Reputation vs authentication<\/h3>\n\n\n\n<p>5.7.1 can indicate either problem:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td>Cause Type<\/td><td>Characteristics<\/td><td>Fix Approach<\/td><\/tr><tr><td>Authentication<\/td><td>Usually fixable immediately<\/td><td>Configure SPF\/DKIM\/DMARC<\/td><\/tr><tr><td>Reputation<\/td><td>Requires sustained effort<\/td><td>Warmup, list cleaning, behavioral change<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>Check your authentication first \u2014 but if that passes and 5.7.1 persists, reputation is the issue.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Why does this error occur?<\/h2>\n\n\n\n<p>Reputation blocks accumulate over time. Understanding the contributing factors helps prioritize your fix.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Low domain\/IP reputation<\/h3>\n\n\n\n<p>Email providers track sender behavior:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/emailwarmup.com\/blog\/emails-going-to-spam\/spam-traps\/\">Spam trap<\/a> hits<\/li>\n\n\n\n<li>Volume patterns (sudden spikes)<\/li>\n\n\n\n<li>Bounce rates (sending to invalid addresses)<\/li>\n\n\n\n<li>Engagement rates (opens, clicks vs. ignores)<\/li>\n\n\n\n<li>Complaint rates (recipients marking mail as spam)<\/li>\n<\/ul>\n\n\n\n<p>Poor metrics across these signals tanks your reputation.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Blacklisting<\/h3>\n\n\n\n<p>Your IP or domain may appear on public blacklists:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>SORBS<\/li>\n\n\n\n<li>Barracuda<\/li>\n\n\n\n<li>Spamhaus<\/li>\n\n\n\n<li>Provider-specific lists<\/li>\n<\/ul>\n\n\n\n<p>Many providers check these lists before accepting mail. One listing can cause widespread delivery failures.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Authentication failure<\/h3>\n\n\n\n<p>Missing or broken authentication contributes to 5.7.1:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>No SPF record<\/li>\n\n\n\n<li>DMARC policy causing rejection<\/li>\n\n\n\n<li>DKIM not signing or signature failing<\/li>\n\n\n\n<li>SPF doesn&#8217;t authorize your sending IP<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Compromised account<\/h3>\n\n\n\n<p>If your email account was hacked and used to send spam, your reputation suffers even after you regain control. The historical damage persists until rebuilt.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Sudden volume spikes<\/h3>\n\n\n\n<p>New domains or IPs sending high volumes immediately trigger suspicion. Providers expect a gradual ramp-up \u2014 sudden spikes signal compromised accounts or spam operations.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Content triggers<\/h3>\n\n\n\n<p>Certain content patterns correlate with spam:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Excessive links<\/li>\n\n\n\n<li>URL shorteners<\/li>\n\n\n\n<li>Known spam phrases<\/li>\n\n\n\n<li>Poor text-to-image ratios<\/li>\n\n\n\n<li>Attachments matching blocked types<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">How do you fix 550 5.7.1?<\/h2>\n\n\n\n<p>Reputation recovery takes time and consistent effort. Start with quick fixes, then address underlying issues.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Implement authentication<\/h3>\n\n\n\n<p>Verify all three mechanisms pass:<\/p>\n\n\n\n<h4 class=\"wp-block-heading\">SPF<\/h4>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Publish an SPF record for your domain<\/li>\n\n\n\n<li>Include all sending IPs (yours and third-party services)<\/li>\n\n\n\n<li>Stay under 10 DNS lookups<\/li>\n\n\n\n<li>Use the <a href=\"https:\/\/emailwarmup.com\/spf-generator\">SPF generator<\/a> if needed<\/li>\n<\/ul>\n\n\n\n<h4 class=\"wp-block-heading\">DKIM<\/h4>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Enable DKIM signing on your mail server or ESP<\/li>\n\n\n\n<li>Publish the public key in DNS<\/li>\n\n\n\n<li>Verify with the <a href=\"https:\/\/emailwarmup.com\/dkim-lookup\">DKIM lookup tool<\/a><\/li>\n<\/ul>\n\n\n\n<h4 class=\"wp-block-heading\">DMARC<\/h4>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Publish a DMARC record (_dmarc.yourdomain.com)<\/li>\n\n\n\n<li>Start with p=none while monitoring<\/li>\n\n\n\n<li>Review aggregate reports for failures<\/li>\n\n\n\n<li>Use the <a href=\"https:\/\/emailwarmup.com\/dmarc-generator\">DMARC generator<\/a> for proper formatting<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Check blacklists<\/h3>\n\n\n\n<p>Search multiple blacklist databases:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Use tools like MXToolbox or the <a href=\"https:\/\/emailwarmup.com\/email-deliverability-test\">email deliverability test<\/a><\/li>\n\n\n\n<li>Note which lists show your IP\/domain<\/li>\n\n\n\n<li>Follow each list&#8217;s<em> <\/em>delisting process<\/li>\n<\/ul>\n\n\n\n<p>Delisting requires fixing the underlying issue first \u2014 lists reject requests if spam behavior continues.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Reduce sending volume<\/h3>\n\n\n\n<p>While reputation recovers:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Pause marketing campaigns<\/li>\n\n\n\n<li>Continue only critical transactional mail<\/li>\n\n\n\n<li>Limit daily volume to 10-20% of normal<\/li>\n\n\n\n<li>Focus sends to engaged recipients<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Clean your list<\/h3>\n\n\n\n<p>Remove addresses that damage reputation:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Hard bounces (invalid addresses)<\/li>\n\n\n\n<li>Spam complainers<\/li>\n\n\n\n<li>Unengaged recipients (no opens in 6+ months)<\/li>\n\n\n\n<li>Purchased or scraped lists (never use these)<\/li>\n<\/ul>\n\n\n\n<p>Proper <a href=\"https:\/\/emailwarmup.com\/blog\/email-deliverability\/email-list-hygiene\/\">email list hygiene<\/a> reduces bounce and complaint rates that feed reputation problems.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Warm your domain<\/h3>\n\n\n\n<p>Gradual volume increase rebuilds trust:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Start with 10-20 emails\/day<\/li>\n\n\n\n<li>Increase 15-20% daily<\/li>\n\n\n\n<li>Send to your most engaged recipients first<\/li>\n\n\n\n<li>Monitor for deferrals signaling throttling<\/li>\n<\/ul>\n\n\n\n<p>Email warmup tools automate this process with realistic engagement patterns.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Request delisting (Gmail)<\/h3>\n\n\n\n<p>Gmail provides a sender contact form for delivery issues:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Visit <a href=\"https:\/\/emailwarmup.com\/blog\/email-deliverability\/google-postmaster-tools\/\">Google&#8217;s Postmaster Tools<\/a><\/li>\n\n\n\n<li>Submit a delivery issue report<\/li>\n\n\n\n<li>Include evidence of fixed authentication and changed behavior<\/li>\n<\/ul>\n\n\n\n<p>Requests without underlying fixes get ignored.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Secure your account<\/h3>\n\n\n\n<p>If a compromise caused the reputation damage:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Scan for malware<\/li>\n\n\n\n<li>Change passwords immediately<\/li>\n\n\n\n<li>Enable two-factor authentication<\/li>\n\n\n\n<li>Check for forwarding rules you didn&#8217;t create<\/li>\n\n\n\n<li>Review connected apps and revoke suspicious ones<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">How do you prevent this error?<\/h2>\n\n\n\n<p>Prevention costs far less than reputation recovery.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Monitor reputation signals<\/h3>\n\n\n\n<p>Track leading indicators before they become blocks:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Gmail Postmaster Tools (<a href=\"https:\/\/emailwarmup.com\/blog\/email-deliverability\/domain-reputation\/\">domain reputation<\/a>, <a href=\"https:\/\/emailwarmup.com\/blog\/email-deliverability\/ip-reputation\/\">IP reputation<\/a>)<\/li>\n\n\n\n<li><a href=\"https:\/\/emailwarmup.com\/blog\/email-deliverability\/microsoft-snds\/\">Microsoft SNDS<\/a> (complaint rates, trap hits)<\/li>\n\n\n\n<li>Engagement metrics (opens, clicks)<\/li>\n\n\n\n<li><a href=\"https:\/\/emailwarmup.com\/blog\/email-deliverability\/email-bounce-rate\/\">Bounce rates<\/a> from your ESP<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Maintain authentication<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Test authentication after any infrastructure change<\/li>\n\n\n\n<li>Monitor DMARC reports for unexpected failures<\/li>\n\n\n\n<li>Update SPF when adding new sending services<\/li>\n\n\n\n<li>Rotate DKIM keys periodically<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Practice list hygiene<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Never purchase email lists<\/li>\n\n\n\n<li>Remove bounces immediately<\/li>\n\n\n\n<li>Verify addresses before import<\/li>\n\n\n\n<li>Use double opt-in for new signups<\/li>\n\n\n\n<li>Sunset unengaged subscribers (6-12 months of no activity)<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Separate mail streams<\/h3>\n\n\n\n<p>Use different IPs or subdomains for:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Transactional mail (receipts, password resets)<\/li>\n\n\n\n<li>Marketing mail (newsletters, promotions)<\/li>\n\n\n\n<li>Cold outreach (if applicable)<\/li>\n<\/ul>\n\n\n\n<p>Reputation problems in one stream won&#8217;t contaminate others.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Monitor and act fast<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Set up alerts for bounce rate spikes<\/li>\n\n\n\n<li>Pause campaigns when metrics deteriorate<\/li>\n\n\n\n<li>Address complaints before they compound<\/li>\n\n\n\n<li>Investigate new blacklist appearances immediately<\/li>\n<\/ul>\n\n\n\n\n<!-- EmailWarmup \u2014 Email Errors Campaign CTA Section -->\n<section id=\"ew-email-errors-consult\" aria-label=\"Help fixing email errors\">\n  <style>\n    \/* Scoped, theme-safe resets *\/\n    #ew-email-errors-consult, #ew-email-errors-consult *{\n      box-sizing:border-box;\n      -webkit-hyphens:none!important; -ms-hyphens:none!important; hyphens:none!important;\n 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Others point to deeper deliverability issues involving authentication, sender reputation, blacklisting, routing, or mailbox provider policy. If you would rather have an expert review it, speak with an\n      <a href=\"https:\/\/emailwarmup.com\/email-deliverability-consultant\">email delieverability consultant<\/a>\n      for free and we can help diagnose the issue and fix it on your behalf.\n    <\/p>\n  <\/div>\n\n  <div class=\"tiles\" role=\"list\">\n    <article class=\"tile t1\" role=\"listitem\">\n      <div class=\"icon\" aria-hidden=\"true\">\n        <svg width=\"18\" height=\"18\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\">\n          <path d=\"M21 15a2 2 0 0 1-2 2H7l-4 4V5a2 2 0 0 1 2-2h14a2 2 0 0 1 2 2z\"><\/path>\n        <\/svg>\n      <\/div>\n      <div>\n        <span class=\"h3like\">Root cause analysis<\/span>\n        <p>We look beyond the error message itself to find what is actually breaking delivery, trust, or inbox placement.<\/p>\n      <\/div>\n    <\/article>\n\n    <article class=\"tile t2\" role=\"listitem\">\n      <div class=\"icon\" aria-hidden=\"true\">\n        <svg width=\"18\" height=\"18\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\">\n          <path d=\"M20 6L9 17l-5-5\"><\/path>\n        <\/svg>\n      <\/div>\n      <div>\n        <span class=\"h3like\">Technical fixes handled for you<\/span>\n        <p>From SPF, DKIM, and DMARC to blacklist cleanup, DNS alignment, and sending setup, we can guide or implement the fix.<\/p>\n      <\/div>\n    <\/article>\n\n    <article class=\"tile t3\" role=\"listitem\">\n      <div class=\"icon\" aria-hidden=\"true\">\n        <svg width=\"18\" height=\"18\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\">\n          <path d=\"M12 20V10\"><\/path>\n          <path d=\"M18 20V4\"><\/path>\n          <path d=\"M6 20v-4\"><\/path>\n        <\/svg>\n      <\/div>\n      <div>\n        <span class=\"h3like\">Deliverability-first review<\/span>\n        <p>We assess whether the error is part of a bigger pattern hurting opens, replies, and overall campaign performance.<\/p>\n      <\/div>\n    <\/article>\n\n    <article class=\"tile t4\" role=\"listitem\">\n      <div class=\"icon\" aria-hidden=\"true\">\n        <svg width=\"18\" height=\"18\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\">\n          <path d=\"M12 12c2.8 0 5-2.2 5-5s-2.2-5-5-5-5 2.2-5 5 2.2 5 5 5z\"><\/path>\n          <path d=\"M2 22c1.5-4 5.5-6 10-6s8.5 2 10 6\"><\/path>\n        <\/svg>\n      <\/div>\n      <div>\n        <span class=\"h3like\">Free expert consultation<\/span>\n        <p>Talk to a real deliverability expert, get honest guidance, and see the next best step without pressure or upsells.<\/p>\n      <\/div>\n    <\/article>\n  <\/div>\n\n  <div class=\"bottom\">\n    <p>\n      <strong>When should you book a consultation?<\/strong> If the error keeps coming back, affects multiple mailboxes or domains, started after an ESP or DNS change, or is tied to spam placement, low inboxing, high bounce rates, or authentication failures, it is usually faster to get an expert involved early.\n    <\/p>\n  <\/div>\n\n  <div class=\"cta\">\n    <a class=\"btn\" href=\"https:\/\/emailwarmup.com\/email-deliverability-consultant\" target=\"_blank\" rel=\"noopener\">\n      Talk to a deliverability expert for free\n      <svg width=\"18\" height=\"18\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" aria-hidden=\"true\">\n        <path d=\"M5 12h14\"><\/path>\n        <path d=\"M12 5l7 7-7 7\"><\/path>\n      <\/svg>\n    <\/a>\n  <\/div>\n<\/section>\n\n\n\n\n\n<h2 class=\"wp-block-heading\">Frequently asked questions<\/h2>\n\n\n\n<p>Here are some commonly asked questions about this error:<\/p>\n\n\n\n<div class=\"schema-faq wp-block-yoast-faq-block\"><div class=\"schema-faq-section\" id=\"faq-question-1773018681538\"><strong class=\"schema-faq-question\">How long does reputation recovery take?<\/strong> <p class=\"schema-faq-answer\">Timeline varies by severity. Minor issues (authentication fixed, small blacklist) may be resolved in days. Severe reputation damage (multiple blacklistings, sustained spam behavior) takes weeks to months of consistent good behavior. Gmail states reputation improves when senders &#8220;meet guidelines and reduce spam rates.&#8221;<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1773018692890\"><strong class=\"schema-faq-question\">Can I still send an email while fixing my reputation?<\/strong> <p class=\"schema-faq-answer\">Yes, but limit volume significantly. Continue essential transactional mail and send to your most engaged recipients. Pause bulk marketing until metrics improve. Continuing high volume with a poor reputation makes recovery harder.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1773018699197\"><strong class=\"schema-faq-question\">Should I change my sending domain?<\/strong> <p class=\"schema-faq-answer\">Starting fresh on a new domain is tempting but risky. Providers track domain-switching behavior as a spam signal. Better to fix the underlying issues and rebuild reputation on your existing domain \u2014 unless the damage is truly irreparable.<\/p> <\/div> <\/div>\n","protected":false},"excerpt":{"rendered":"<p>The 550 5.7.1 error means the receiving server blocked your message due to low sender reputation \u2014 your domain or IP is flagged for spam-like behavior.\u00a0 Fix it by implementing proper SPF\/DKIM\/DMARC authentication, checking blacklist status, reducing volume, and rebuilding trust through gradual email warmup. Unlike addressing errors (5.1.x) or mailbox state errors (5.2.x), the [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":5202,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","footnotes":""},"categories":[38],"tags":[],"class_list":["post-5201","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-email-errors"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v25.0 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>How To Fix 550 5.7.1 | Message Blocked [Low Domain Reputation]<\/title>\n<meta name=\"description\" content=\"The 550 5.7.1 error means the receiving server blocked your message due to low sender reputation. 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