{"id":5262,"date":"2026-03-10T02:23:14","date_gmt":"2026-03-10T02:23:14","guid":{"rendered":"https:\/\/emailwarmup.com\/blog\/?p=5262"},"modified":"2026-03-10T02:23:16","modified_gmt":"2026-03-10T02:23:16","slug":"how-to-fix-450-4-2-1-mailbox-temporarily-unavailable-greylisted","status":"publish","type":"post","link":"https:\/\/emailwarmup.com\/blog\/email-errors\/how-to-fix-450-4-2-1-mailbox-temporarily-unavailable-greylisted\/","title":{"rendered":"How To Fix 450 4.2.1 | Mailbox Temporarily Unavailable \u2013 Greylisted"},"content":{"rendered":"\n<figure class=\"wp-block-image size-full\"><img fetchpriority=\"high\" decoding=\"async\" width=\"3112\" height=\"1980\" src=\"https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg\" alt=\"450 4.2.1\" class=\"wp-image-5263\"\/><\/figure>\n\n\n\n<p>The 450 4.2.1 error means the recipient&#8217;s server is <em>greylisting<\/em> your email \u2014 temporarily rejecting unknown senders to filter spam.&nbsp;<\/p>\n\n\n\n<p>Fix it by simply waiting 15-30 minutes and letting your mail server retry automatically. Greylisting is a spam prevention technique, not a permanent block.<\/p>\n\n\n\n<p>Greylisting works because spammers rarely retry \u2014 they blast once and move on. Legitimate mail servers retry after temporary failures, eventually delivering the message.&nbsp;<\/p>\n\n\n\n<p>The inconvenience is intentional \u2014 the brief delay filters spam effectively. However, proper authentication (SPF, DKIM, DMARC) often bypasses greylisting entirely.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Quick skim \u2014 450 4.2.1 error overview<\/h2>\n\n\n\n<p>The 450 4.2.1 error indicates intentional temporary rejection for spam filtering.<\/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>450 4.2.1<\/td><\/tr><tr><td>Category<\/td><td>Greylisting \/ temporary rejection<\/td><\/tr><tr><td>Meaning<\/td><td>Unknown sender temporarily deferred<\/td><\/tr><tr><td>Severity<\/td><td>Temporary (resolves on retry)<\/td><\/tr><tr><td>Common causes<\/td><td>First contact, missing authentication, anti-spam policy<\/td><\/tr><tr><td>Fix approach<\/td><td>Wait \u2192 auto-retry \u2192 verify authentication<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">What does greylisting mean?<\/h2>\n\n\n\n<p>Greylisting temporarily rejects emails from unknown senders based on the triplet: sender IP + sender email + recipient email. The first attempt from a new triplet receives 450 (try again later). Subsequent attempts from the same triplet \u2014 after a waiting period \u2014 succeed.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Why it works<\/h3>\n\n\n\n<p>Spam infrastructure differs from legitimate mail servers:<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td>Behavior<\/td><td>Spam Systems<\/td><td>Legitimate Systems<\/td><\/tr><tr><td>Retry after 450<\/td><td>Rarely<\/td><td>Always<\/td><\/tr><tr><td>Volume per IP<\/td><td>High<\/td><td>Moderate<\/td><\/tr><tr><td>Unique triplets<\/td><td>Many<\/td><td>Fewer<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>Spammers blast millions of messages \u2014 they don&#8217;t wait and retry. Legitimate servers follow RFC standards and retry temporary failures.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Greylist timeline<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td>Event<\/td><td>Timing<\/td><\/tr><tr><td>First attempt<\/td><td>Rejected with 450<\/td><\/tr><tr><td>Waiting period<\/td><td>15-30 minutes (varies by server)<\/td><\/tr><tr><td>Second attempt<\/td><td>Accepted (triplet now known)<\/td><\/tr><tr><td>Future emails<\/td><td>Pass immediately (triplet cached)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">Why does this error occur?<\/h2>\n\n\n\n<p>Greylisting triggers when the receiving server doesn&#8217;t recognize your sending triplet.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">First contact<\/h3>\n\n\n\n<p>Your server hasn&#8217;t sent to this recipient before (or recently):<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>New business relationship<\/li>\n\n\n\n<li>Changed sending infrastructure<\/li>\n\n\n\n<li>Recipient switched email providers<\/li>\n\n\n\n<li>Greylist cache expired<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Missing authentication<\/h3>\n\n\n\n<p>Authenticated senders often bypass greylisting:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Policy varies by recipient server configuration<\/li>\n\n\n\n<li>Properly authenticated mail may skip greylist entirely<\/li>\n\n\n\n<li>SPF\/DKIM\/DMARC failures increase greylist likelihood<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Rate limiting variation<\/h3>\n\n\n\n<p>Some servers use 450 4.2.1 for rate limiting (similar to greylisting):<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Volume exceeded threshold<\/li>\n\n\n\n<li>Sending too fast to this server<\/li>\n\n\n\n<li>Behavior triggered anti-spam measures<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">How do you fix 450 4.2.1?<\/h2>\n\n\n\n<p>For genuine greylisting, the fix is simple: wait.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Wait and auto-retry<\/h3>\n\n\n\n<p>Your mail server handles this automatically:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Server queues the deferred message<\/li>\n\n\n\n<li>Retries after configured interval (typically 15-60 minutes)<\/li>\n\n\n\n<li>Delivery succeeds on retry<\/li>\n\n\n\n<li>No manual intervention needed<\/li>\n<\/ol>\n\n\n\n<p>Check your mail queue if concerned \u2014 the message should show &#8220;deferred&#8221; status, not &#8220;failed.&#8221;<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Verify authentication<\/h3>\n\n\n\n<p>Proper authentication reduces greylisting frequency:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Confirm <a href=\"https:\/\/emailwarmup.com\/blog\/email-authentication\/spf-record\/\">SPF record<\/a> authorizes your IP<\/li>\n\n\n\n<li>Verify <a href=\"https:\/\/emailwarmup.com\/blog\/email-authentication\/dkim\">DKIM signatures<\/a> are valid<\/li>\n\n\n\n<li>Check <a href=\"https:\/\/emailwarmup.com\/blog\/email-authentication\/dmarc\">DMARC alignment<\/a> passes<\/li>\n<\/ul>\n\n\n\n<p>Authenticated senders build reputation faster, reducing greylist triggers.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Reduce message size<\/h3>\n\n\n\n<p>Large messages sometimes trigger 450 responses:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Compress attachments<\/li>\n\n\n\n<li>Use cloud links for large files<\/li>\n\n\n\n<li>Split content across multiple messages if necessary<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Check recipient status<\/h3>\n\n\n\n<p>The 450 code sometimes indicates actual mailbox issues:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Mailbox temporarily full<\/li>\n\n\n\n<li>Recipient account suspended<\/li>\n\n\n\n<li>Server undergoing maintenance<\/li>\n<\/ul>\n\n\n\n<p>If retries consistently fail, contact the recipient through alternate channels.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">When should you escalate?<\/h2>\n\n\n\n<p>Greylisting should resolve within 1-2 hours. Escalate if:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Error persists across different senders<\/li>\n\n\n\n<li>Multiple recipients at same domain affected<\/li>\n\n\n\n<li>Pattern appears across your entire sending infrastructure<\/li>\n\n\n\n<li>Message remains deferred after 24 hours<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Contact recipient<\/h3>\n\n\n\n<p>Ask them to:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Whitelist your sending domain or IP<\/li>\n\n\n\n<li>Check if their IT department can add you to an allow list<\/li>\n\n\n\n<li>Verify their mailbox is functioning<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Verify sender infrastructure<\/h3>\n\n\n\n<p>Check your side:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Run an <a href=\"https:\/\/emailwarmup.com\/email-deliverability-test\">email deliverability test<\/a><\/li>\n\n\n\n<li>Verify authentication passes<\/li>\n\n\n\n<li>Check <a href=\"https:\/\/emailwarmup.com\/blog\/email-blacklist\/how-to-check-if-your-email-is-blacklisted\/\">blacklist status<\/a><\/li>\n\n\n\n<li>Review sending patterns<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">How do you minimize greylisting impact?<\/h2>\n\n\n\n<p>Proper configuration reduces greylist triggers across your sending.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Maintain authentication<\/h3>\n\n\n\n<p>Well-authenticated senders face less scrutiny:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Keep SPF, DKIM, and DMARC properly configured<\/li>\n\n\n\n<li>Monitor authentication pass rates<\/li>\n\n\n\n<li>Fix failures promptly<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Build sender reputation<\/h3>\n\n\n\n<p>Consistent, legitimate sending builds trust:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Keep bounce rates low<\/li>\n\n\n\n<li>Minimize <a href=\"https:\/\/emailwarmup.com\/blog\/emails-going-to-spam\/spam-complaints\/\">spam complaints<\/a><\/li>\n\n\n\n<li>Maintain steady volume (avoid spikes)<\/li>\n\n\n\n<li>Use <a href=\"https:\/\/emailwarmup.com\/\">email warmup<\/a> for new infrastructure<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Use a reliable sending infrastructure<\/h3>\n\n\n\n<p>Reputable IPs bypass greylisting more often:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Dedicated IPs build your own reputation<\/li>\n\n\n\n<li>Established ESPs have a known-good reputation<\/li>\n\n\n\n<li>Avoid free\/shared infrastructure for business email<\/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; 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}\n    #ew-email-errors-consult .btn:active{ transform:translateY(1px); }\n\n    @media (max-width:640px){\n      #ew-email-errors-consult .title{ font-size:24px; }\n    }\n  <\/style>\n\n  <div class=\"intro\">\n    <div class=\"eyebrow\">Need help fixing an email error?<\/div>\n    <h2 class=\"title\">Still stuck after trying the fix?<\/h2>\n    <p class=\"subtitle\">\n      Some email errors are easy to clear. 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-1773109236965\"><strong class=\"schema-faq-question\">Is 450 4.2.1 a hard bounce or a soft bounce?<\/strong> <p class=\"schema-faq-answer\">Soft bounce \u2014 the message is deferred, not rejected. Your mail server queues it and retries. Most greylisted messages deliver successfully on the second or third attempt. No action needed unless retries are exhausted without success.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1773109243338\"><strong class=\"schema-faq-question\">Why does greylisting delay time-sensitive emails?<\/strong> <p class=\"schema-faq-answer\">Unfortunately, that&#8217;s the tradeoff. Greylisting sacrifices speed for spam filtering. For time-sensitive communications, ensure proper authentication (often bypasses greylisting) or pre-establish relationships with regular communication.<\/p> <\/div> <div class=\"schema-faq-section\" id=\"faq-question-1773109249566\"><strong class=\"schema-faq-question\">Can I disable greylisting on the recipient&#8217;s end?<\/strong> <p class=\"schema-faq-answer\">Only if you control the receiving server. Greylisting is a recipient-side policy. You can ask recipients to whitelist your domain, but you cannot disable their spam protection. Proper authentication is your best strategy for minimizing greylisting impact.<\/p> <\/div> <\/div>\n","protected":false},"excerpt":{"rendered":"<p>The 450 4.2.1 error means the recipient&#8217;s server is greylisting your email \u2014 temporarily rejecting unknown senders to filter spam.&nbsp; Fix it by simply waiting 15-30 minutes and letting your mail server retry automatically. Greylisting is a spam prevention technique, not a permanent block. Greylisting works because spammers rarely retry \u2014 they blast once and [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":5263,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","footnotes":""},"categories":[38],"tags":[],"class_list":["post-5262","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 450 4.2.1 | Mailbox Temporarily Unavailable [Greylisted]<\/title>\n<meta name=\"description\" content=\"The 450 4.2.1 error means the recipient&#039;s server is greylisting your email \u2014 temporarily rejecting unknown senders to filter spam.\u00a0Let&#039;s fix!\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link 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No action needed unless retries are exhausted without success.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/emailwarmup.com\/blog\/email-errors\/how-to-fix-450-4-2-1-mailbox-temporarily-unavailable-greylisted\/#faq-question-1773109243338","position":2,"url":"https:\/\/emailwarmup.com\/blog\/email-errors\/how-to-fix-450-4-2-1-mailbox-temporarily-unavailable-greylisted\/#faq-question-1773109243338","name":"Why does greylisting delay time-sensitive emails?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"Unfortunately, that's the tradeoff. Greylisting sacrifices speed for spam filtering. For time-sensitive communications, ensure proper authentication (often bypasses greylisting) or pre-establish relationships with regular communication.","inLanguage":"en-US"},"inLanguage":"en-US"},{"@type":"Question","@id":"https:\/\/emailwarmup.com\/blog\/email-errors\/how-to-fix-450-4-2-1-mailbox-temporarily-unavailable-greylisted\/#faq-question-1773109249566","position":3,"url":"https:\/\/emailwarmup.com\/blog\/email-errors\/how-to-fix-450-4-2-1-mailbox-temporarily-unavailable-greylisted\/#faq-question-1773109249566","name":"Can I disable greylisting on the recipient's end?","answerCount":1,"acceptedAnswer":{"@type":"Answer","text":"Only if you control the receiving server. Greylisting is a recipient-side policy. You can ask recipients to whitelist your domain, but you cannot disable their spam protection. Proper authentication is your best strategy for minimizing greylisting impact.","inLanguage":"en-US"},"inLanguage":"en-US"}]}},"uagb_featured_image_src":{"full":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",3112,1980,false],"thumbnail":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",150,95,false],"medium":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",300,191,false],"medium_large":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",768,489,false],"large":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",1024,652,false],"1536x1536":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",1536,977,false],"2048x2048":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",2048,1303,false],"profile_24":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",24,15,false],"profile_48":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",48,31,false],"profile_96":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",96,61,false],"profile_150":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",150,95,false],"profile_300":["https:\/\/emailwarmup.com\/blog\/wp-content\/uploads\/2026\/03\/450-4.2.1_11zon.jpg",300,191,false]},"uagb_author_info":{"display_name":"Daniyal Dehleh","author_link":"https:\/\/emailwarmup.com\/blog\/author\/daniyaldehleh\/"},"uagb_comment_info":0,"uagb_excerpt":"The 450 4.2.1 error means the recipient&#8217;s server is greylisting your email \u2014 temporarily rejecting unknown senders to filter spam.&nbsp; Fix it by simply waiting 15-30 minutes and letting your mail server retry automatically. Greylisting is a spam prevention technique, not a permanent block. Greylisting works because spammers rarely retry \u2014 they blast once and&hellip;","_links":{"self":[{"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/posts\/5262","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/comments?post=5262"}],"version-history":[{"count":1,"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/posts\/5262\/revisions"}],"predecessor-version":[{"id":5264,"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/posts\/5262\/revisions\/5264"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/media\/5263"}],"wp:attachment":[{"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/media?parent=5262"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/categories?post=5262"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/emailwarmup.com\/blog\/wp-json\/wp\/v2\/tags?post=5262"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}