Email deliverability, fixed
Why your mail bounces, gets deferred, or lands in spam — and the exact steps to get it back in the inbox. Start with the fix for the problem you have, or test your domain in 30 seconds.
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GrokDeliverability is whether your email reaches the inbox — not just whether the server accepts it. Every delivery problem traces back to one of three things: authentication, reputation, or engagement. Get all three right and your mail lands; break any one and you get a bounce, a deferral, or the spam folder.
Authentication proves who sent the message. Publish SPF, sign with DKIM, and set a DMARC policy so the passing domain aligns with your visible From address. Since 2024, Gmail and Yahoo reject bulk mail that skips this, and Microsoft returns a 550 5.7.x bounce for the same reason.
Reputation is how mailbox providers rate your sending IP and domain based on history: complaint rates, spamtrap hits, bounce rates, and whether your IP has landed on a blocklist. A damaged reputation shows up as 4xx deferrals and spam placement even when your DNS is perfect.
Engagement decides the last mile — which tab you land in and whether you stay out of spam over time. The guides below work through the specific errors and placements you are most likely to hit, each with the exact fix.
Start with your problem
The most common deliverability failures, each with a step-by-step fix.
Why is Microsoft 365 rejecting my email with a 550 5.7.x error?
Microsoft 365 returns 550 5.7.x when your mail fails a policy or authentication check. Fix SPF, DKIM, and DMARC alignment to clear the access-denied bounce.
Read the fix →What does SMTP error 421 mean and how do I fix it?
SMTP error 421 is a temporary deferral, not a bounce. Fix it by slowing your send rate and authenticating mail with SPF, DKIM, and DMARC before retrying.
Read the fix →Why do my emails land in Gmail's Promotions tab?
Gmail sorts marketing-style mail into Promotions using content, sender and engagement signals — not spam. Here is how the tabs work and how to reach Primary.
Read the fix →Why is Gmail rejecting my emails with a 550 error?
Gmail 550 5.7.26 rejections mean your mail fails authentication. See why Google now rejects instead of defers, and the exact fixes to get delivered.
Read the fix →Why is Yahoo blocking my emails as unauthenticated?
Yahoo blocks unauthenticated mail because SPF, DKIM, or DMARC failed. Fix the 550 5.7.9 'sender is unauthenticated' bounce by authenticating and aligning.
Read the fix →Why is my email queued and how do I fix it?
Email stuck on 'Queued'? It means your message is waiting to send, not failed. See what causes it in Gmail and on mail servers — and how to fix each one.
Read the fix →Fix delivery to a specific provider
Blocked or junked by one mailbox provider? Each guide covers that provider's real rules, reputation tools, and the exact fix.
Why are my emails being blocked?
Emails get blocked for four main reasons: your domain fails SPF, DKIM, or DMARC checks, your spam complaint rate crossed the provider's threshold, your IP or domain sits on a blocklist, or you broke a bulk-sender rule. Read the bounce to identify the provider, fix authentication first, then check blocklists and complaint data.
Read the fix →Why is Outlook blocking my emails?
Outlook blocks outbound mail for three reasons: your domain fails SPF, DKIM, or DMARC checks; your sending IP or domain has a poor reputation with Microsoft's SmartScreen filter; or your IP sits on a Microsoft block list. Fix authentication first, then check SNDS and request delisting; most blocks trace back to those three.
Read the fix →How to stop emails going to spam in Outlook
To stop emails going to spam in Outlook, fix the four things Microsoft's filter actually scores: authentication that passes but doesn't align with your From domain, a rising junk-complaint rate, weak list hygiene and content signals, and a cold IP or domain with no sending history. Align SPF and DKIM first; that is the post-May-2025 junk trigger.
Read the fix →Why do emails go to junk in Hotmail and Outlook?
Emails go to junk in Hotmail and Outlook.com when Microsoft's SmartScreen filter distrusts the sender: missing or misaligned SPF, DKIM, or DMARC, a high junk-complaint rate, a new IP with no history, or a stale mailing list. Since May 2025, Microsoft's high-volume sender requirements make failing authentication a documented enforcement trigger: Junk placement first, then rejection. Fix authentication first; reputation follows.
Read the fix →Why does Outlook move emails to junk after they arrive?
Outlook moves delivered mail to Junk after arrival for four main reasons: Microsoft's zero-hour auto purge (ZAP) re-scans the last 48 hours of delivered mail against updated spam and phishing signatures; the recipient marked you as junk, so every future message is classified as spam; the Outlook desktop client's own junk filter re-files it; or a recipient rule moves it. Authentication and complaint rate decide the first two.
Read the fix →Why is Microsoft 365 blocking outbound emails?
Microsoft 365 blocks outbound mail for three reasons: a user or connector exceeded outbound sending limits and landed on the Restricted entities page; Exchange Online classified the mail as spam and routed it through the high-risk delivery pool; or the tenant hit Exchange Online's service limits. Recipient-side rejections trace to missing SPF, DKIM, or DMARC.
Read the fix →Why is Microsoft blocking my automated emails?
Microsoft blocks automated mail (scanners, CRMs, monitoring alerts) for three reasons: the app or device fails SPF and DKIM alignment for your domain; it uses a submission method the tenant no longer accepts, like Direct Send or Basic-auth SMTP; or it trips Exchange Online throttling. The Office 365 mail filter treats unauthenticated app mail as anonymous internet traffic.
Read the fix →Why are my emails going to spam in Gmail?
Gmail spam-folders outbound mail for four main reasons: SPF, DKIM, or DMARC is missing or unaligned under Google's Email sender guidelines; your user-reported spam rate crossed 0.3%; your domain reputation in Google Postmaster Tools is Low or Bad; or you send bulk mail without one-click unsubscribe. Fix authentication first; everything else builds on it.
Read the fix →Why does Gmail mark new domain emails as spam?
Gmail spam-folders mail from a new domain because the domain has no sending history, so authentication and behavior are the only signals Google can score. Missing SPF, DKIM, or DMARC, a cold start at full volume, and a bare domain with no web presence all read as spam. Authenticate everything first, then warm up gradually.
Read the fix →Your email has been blocked because the sender is unauthenticated: the Gmail fix
Gmail returns "blocked because the sender is unauthenticated" when a message passes neither SPF nor DKIM for your domain. Under Google's February 2024 sender requirements, unauthenticated mail is spam-foldered or, as here, refused outright. The fix is DNS: publish SPF and DKIM for every service that sends as your domain, confirm both pass and align, then re-send.
Read the fix →Why is Yahoo blocking my emails?
Yahoo blocks outbound mail for three main reasons: your domain fails SPF, DKIM, or DMARC under the sender requirements Yahoo has enforced since February 2024; your spam complaint rate is above Yahoo's published 0.3% ceiling; or your IP has a poor reputation or sits on a blocklist Yahoo consults. AOL runs on the same filters, so one fix clears both.
Read the fix →Why is iCloud blocking my emails?
iCloud Mail blocks outbound mail for three main reasons: your sending IP is flagged by Proofpoint's reputation system (a linkage neither vendor documents, but one deliverability teams widely report in iCloud bounces), your domain fails SPF, DKIM, or DMARC, or your stream breaks one of Apple's published bulk-sender rules. Fix authentication first, check the IP at Proofpoint's lookup, then escalate to Apple's postmaster address.
Read the fix →Deliverability questions, answered straight
Benchmark and how-it-works questions, each answered with cited vendor data and a fix.
What is a good email bounce rate?
Under 1% is healthy, 2% needs investigating, 5%+ is an emergency. The bounce-rate benchmarks ESPs actually publish, plus the triage table to fix yours.
Read the answer →Why are my Mailchimp emails going to spam?
Mailchimp campaigns landing in spam? The four real causes: unauthenticated sending domain, shared IP reputation, list decay, engagement. And the DNS fix.
Read the answer →How to authenticate email for marketing
The platform-agnostic setup order: sending subdomain, SPF include, custom DKIM, DMARC with rua, alignment check, policy ramp. With live ESP doc links.
Read the answer →What is SPF flattening?
SPF flattening swaps include: mechanisms for raw IPs to beat the 10-lookup limit. When it helps, when it silently breaks, and the alternatives that age better.
Read the answer →Why are my newsletters going to spam?
Four causes: failed SPF/DKIM/DMARC, no one-click unsubscribe, complaints over 0.3%, dead engagement. What Gmail and Yahoo actually require, plus the fix.
Read the answer →What is Google Postmaster Tools?
Google Postmaster Tools explained: the v2 dashboards, DNS TXT setup, the 0.3% spam-rate line, and how to read it before moving DMARC to p=reject.
Read the answer →What is Microsoft SNDS?
SNDS is Microsoft's free per-IP reputation portal for Outlook.com senders. What it shows, how to sign up, its limits, and how it pairs with DMARC reports.
Read the answer →What are DMARC aggregate reports?
Daily XML files sent to your rua address: every source IP, message counts, disposition, SPF/DKIM results. What's inside one and how to read it.
Read the answer →Why is DMARC failing but SPF passes?
SPF checks the Return-Path domain; DMARC needs it to match your From domain. Why ESP bounce domains, forwarding, and strict aspf break alignment.
Read the answer →How do I move from DMARC p=none to p=reject?
The staged playbook from p=none to p=reject: monitor with rua, fix alignment per sender, ramp pct through quarantine, then enforce. Timelines and rollback.
Read the answer →Does DMARC affect email marketing?
Yes. Google and Microsoft require DMARC for bulk senders, misalignment sends campaigns to spam, and enforcement unlocks your BIMI logo in the inbox.
Read the answer →Why did my email get clipped in Gmail?
Gmail clips HTML over ~102KB behind a View entire message link. What counts toward the limit, why it hurts opens and unsubscribes, and how to slim the template.
Read the answer →Decoding a bounce message?
Match the exact code in the bounce — 550 5.7.26, 554 5.7.1, 421 4.7.0 — to what it means, who's at fault, and the step-by-step fix.
Look up your SMTP error codeDiagnose your domain in one pass
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