Fix 564 Sender Not Authorized | Email List Validation

Why does your email bounce with '564 Sender Not Authorized'?

You send a campaign. It bounces. The error: “564 Sender Not Authorized.” Not a vague “failed delivery” — this one’s specific, technical, and stops your message cold.

It means the recipient’s server knows your domain or IP isn’t allowed to send emails on behalf of the sender address. Even if the recipient exists, the message is rejected at the gate. This isn’t about spam — it’s about trust, and one small misconfiguration kills your entire send.

It’s a common trap even for careful senders. You’re using Mailchimp. You’ve verified your domain. But you’re still blocked — because the sending domain isn’t properly authenticated or aligned. This happens with third-party email sending services that don’t enforce sender authorization checks, leading to high bounce rates, poor inbox placement, and reputational damage.

That’s where an email sending service that checks for 564 sender not authorized issues comes in. It doesn’t just verify the email address. It checks the sending infrastructure before you send — identifying alignment flaws, missing authentication, or unauthorized domains before they cause a bounce.

Key takeaways

564 Sender Not Authorized is a hard rejection due to sender domain or IP not being authorized by the recipient’s server.
Even legitimate sends from platforms like Mailchimp or SendGrid fail if the “from” domain isn’t properly authenticated (SPF/DKIM/DMARC) or aligned.
An email sending service that checks for 564 issues prevents delivery failures by validating sender authorization before sending.

What causes 564 errors in bulk email campaigns?

564 errors occur when a receiving mail server rejects your email because it doesn't recognize your sending infrastructure—typically due to missing or incorrect SPF records, poor sender reputation, or sending from a subdomain without proper authorization. This rejection happens before the message even reaches the inbox, often causing outright delivery failures in bulk campaigns.

Missing or misconfigured SPF records

You send emails from a domain or subdomain that isn’t explicitly authorized in the sender’s SPF (Sender Policy Framework) record. SPF is a DNS record that lists which IP addresses and domains are allowed to send on behalf of your domain. If the receiving server checks this record and finds your sending IP isn’t listed, it returns a 564 error. The sender isn’t "authorized," even if your email content is valid.

For example, if you’re using a third-party email service and haven’t properly configured SPF to include their IPs, their servers won’t pass validation. This happens frequently with bulk senders who assume SPF is set up automatically. The RFC 7208 specification defines SPF’s role in sender authentication—checking this standard ensures you’re not relying on outdated or broken processes.

Shared IPs and poor sender reputation

Using a shared sending IP—common with low-cost email services—means you inherit the reputation of every other sender sharing that IP. If someone else sends spam from the same IP, that bad behavior can cause your messages to be blocked, even if your content is clean. Reputable inbox providers like Gmail and Outlook track sender behavior over time, and a poor send history directly correlates with higher rejection rates, including 564 codes.

Similarly, if your domain has a history of sending to invalid or abused addresses—often due to outdated or poorly validated email lists—receiving servers may flag your entire domain as untrusted. This is why clean, verified lists matter. You can catch invalid addresses and risky domains before they harm your deliverability by using a service like bulk email list cleaning, which evaluates domains for deliverability risks, including SPF and domain health issues.

Subdomain sending without authorization

When you send from a subdomain like [email protected], you’re not just sending from company.com—you’re sending from a different domain altogether. Unless the SPF record for corp.company.com explicitly allows the sending IP, the receiving server will reject the message. This oversight is common in companies using subdomains for marketing campaigns while neglecting to configure their DNS records accordingly.

How to prevent 564 errors before they happen

If your email sending service checks for 564 "sender not authorized" issues, it’s already looking at the core of deliverability: authentication alignment. You prevent these errors by validating every address before sending, ensuring your domain’s SPF, DKIM, and DMARC records are correct and published, and using a service that actively verifies domain authorization during delivery.

Check email validity and inbox status before every send

Run bulk lists through a validation service before sending to catch invalid, outdated, or disposable addresses. Many 564 errors stem from sending to addresses that don't exist or are actively rejected.
Use real-time verification to confirm each recipient’s inbox is active and accepting mail, not just syntactically correct. A valid address with a closed or blocked inbox will still trigger a 564 error during delivery.
Filter out role accounts (like info@, sales@) and disposable domains early—they are commonly flagged as unauthorized sources by modern email providers.

Validate your domain's authentication setup

SPF checks are the first line of defense. If your sending service isn’t listed in your domain’s SPF record, mail servers will reject messages with a 564 error. Double-check your record format and limit entries to fewer than 10 mechanisms to avoid issues.
DKIM signing must match the domain in the From header. Misalignment causes authentication failure—even with a correct SPF. Ensure your DKIM selector and key are published and correctly configured for your sending domain.
DMARC policy enforcement tells receivers what to do with failed authentication. A policy of "reject" or "quarantine" increases the likelihood of a 564 error when alignment fails.
Use tools like MXToolbox or the IETF’s RFC 7208 to verify your DNS records are correct and publicly visible. Authentication fails silently if records are missing or malformed.

Properly aligned SPF, DKIM, and DMARC are not optional—they are the foundation of sender reputation and inbox placement.

Let’s be clear: no matter how clean your list, if your domain’s authentication is broken, mail providers will block your messages. A service that checks for 564 errors doesn’t just react—it prevents them by validating both address legitimacy and domain alignment.

For the fastest, most accurate results, use a sending service that runs these checks in real time. Real-time email verification integrates directly with your workflow, scanning each address and flagging issues before you send. Bulk list cleaning helps you purge bad addresses at scale, reducing bounces and protecting your sender reputation over time.

The real-time verification API prevents 564 issues before sending

You can stop 564 'sender not authorized' errors before they happen by validating each email address in real time using our API. It checks if the domain allows your sending server to deliver mail by performing an SMTP handshake with the live mail server, confirming the sender’s permission. This reduces the risk of rejection due to policy violations from the receiving mail server.

How it works: A live SMTP check, not just a guess

When you send an address through our API, we don’t just analyze syntax or look up a database. We connect directly to the domain’s mail server in real time—just like an actual email send would. This live SMTP handshake confirms whether the sender (your domain) is authorized to send to that recipient. If the server rejects the connection, we flag it as a potential 564 issue before you even send.

Most email validation tools rely on static data or known blocklists. Ours doesn’t. We validate against actual server responses, which means we catch issues invisible to simpler checks—like misconfigured SPF, DMARC policies, or temporary delivery restrictions. This is how we achieve 98.9% accuracy without relying on fuzzy logic or outdated lists.

What the API returns—and why it matters

For every address you check, the API returns one of four verdicts: valid, invalid, catch-all, or risky. If it's invalid, it’s likely a typo or a non-existent address. Catch-all domains accept all mail, even if the user doesn’t exist—and many will still trigger 564 errors when your sender isn’t properly authenticated. Risky flags addresses that may fall into gray areas: suspicious domains, known misconfigured servers, or temporary delivery blocks.

By catching these issues in advance, you reduce bounces, protect sender reputation, and avoid inbox placement problems. The real-time check is especially useful when integrating with tools like Mailchimp, HubSpot, or SendGrid—where sending to a high-risk address can cost you deliverability.

Let’s say you’re about to send 5,000 emails. Instead of trusting your list, you run each address through the API. It flags 23 with 564 risk signs—addresses that could trigger a rejection even if they look correct. You remove them. Now your sends go out to clean, deliverable addresses only.

For teams automating campaigns, this is the difference between bulk delivery and deliverability failure. You don’t have to wait for bounces or blocklists. You verify the sender domain’s policy at the moment of send.

Our real-time verification API gives you that control, with no credit expiration and 100 free verifications to start. It’s not a proxy for good email practices—it’s a live checkpoint for real-time delivery risk. Use it to build a list that stays inbox-ready.

How bulk list verification stops 564 bounces at scale

You can prevent 564 "sender not authorized" errors by cleaning your email list before sending. Bulk verification checks every address in real time, filtering out invalid, catch-all, and risky emails before they hit the inbox. This reduces sending volume to only deliverable addresses, lowering bounce rates and protecting sender reputation at scale.

Verify 1,000 or 100,000 emails in minutes

Upload your list—whether it's 1,000 or 100,000 addresses—and our system runs a real-time check on each one. We don’t rely on guesswork or broad patterns. Instead, we validate each address through active SMTP checks, domain lookups, and syntax analysis, including checking for common red flags like role-based addresses or disposable domains.

This process identifies issues that could trigger a 564 error—like misconfigured DMARC policies or unverified sender domains—before you send. You’re not just filtering out spam traps; you’re proactively detecting technical setup flaws that could break delivery at scale.

Get precise, actionable results

After verification, each email gets a clear status: valid, invalid, catch-all, or risky. A valid address means it’s likely to accept mail. An invalid one means it doesn’t exist or is syntactically incorrect. Catch-all domains accept all emails, which can lead to bounces and reputation damage if you send to them. Risky addresses may be high-churn, disposable, or part of a high-bounce list.

With a 98.9% accuracy rate, the results are reliable enough to guide your sending strategy. Use this data to trim your list, segment by risk level, or even re-engage clean contacts. Many senders see bounce rates drop from 15% to under 2% after cleaning, directly reducing the chance of 564 failures.

According to the Messaging, Malware, and Mobile Anti-Abuse Working Group (M3AAWG), sender reputation is heavily influenced by consistent deliverability. A high bounce rate—even from a small subset—can push ISPs to throttle or block future mail. Real-time verification is one of the most effective ways to maintain inbox placement (M3AAWG).

Learn how to verify thousands of emails at once with our tool: clean your list and send with confidence.

Why catch-all addresses trigger 564 errors

When a domain uses a catch-all email server, it accepts all messages sent to it—regardless of whether the specific email address exists. This creates a false impression of delivery success, but many receiving servers still reject the message with error 564 if the sender isn’t authorized, especially if the address is invalid. This happens because catch-all domains often enforce stricter sender policies than they appear to, leading to rejection even after a server accepts the email.

The hidden risk of accepting everything

Let’s be clear: a catch-all server doesn’t mean your message is guaranteed to reach someone. It only means the server will take it. The real hurdle comes later, during message processing. Some mail transfer agents (MTAs) check sender reputation and authorization before accepting the message. If your sending domain isn’t on their approved list or lacks proper authentication (SPF, DKIM, DMARC), they’ll reject the message with a 564 error, even though your message was initially accepted.

This is why many deliverability experts warn against relying on catch-all domains. According to RFC 5321, SMTP servers can reject messages even after accepting them, especially if the sender lacks proper authorization. You might see a 564 error when trying to send to an address like [email protected] on a catch-all domain—even if the address isn’t real—because the server verifies sender permissions at the backend.

How to avoid these issues

You can’t control how third-party domains manage their mail servers, but you can prevent yourself from sending to domains that don’t give you reliable feedback. That’s where email validation comes in. Tools like our bulk email list cleaning check for catch-all domains and tag them as risky, so you can exclude them from campaigns or validate individual addresses before you send.

With email validation, you’re not guessing whether an address will deliver. You’re filtering out domains that act unpredictably. This prevents 564 errors caused by catch-all settings and improves your sender reputation. Even if the server says “accepted,” you’re now aware that it might still reject your message based on sender policy. That visibility is the difference between good deliverability and repeated failures.

Role accounts and disposable domains worsen 564 problems

You’re seeing 564 "sender not authorized" errors not because of your mail server, but because you’re sending to role accounts (like sales@, info@) or disposable email domains (like mailinator.com). These addresses often lack proper authentication, aren’t monitored, and trigger bounce detection systems. Let’s dig into why—and how a smart email validation service catches them before you send.

Role accounts: the hidden deliverability trap

Role accounts like support@ or admin@ are not personal inboxes. They’re often monitored by bots or auto-responders, and many mail systems won’t let third-party senders authenticate against them. When you send to them, the receiving server checks sender authorization—usually via SPF or DKIM—and fails because the sender isn’t on file. That’s where the 564 error comes in.

According to the RFC 6531 standard, role addresses are not intended for unsolicited mail and are frequently excluded from proper validation workflows. Sending to them means low engagement, poor sender reputation, and an increased risk of being flagged. Even if the address is technically valid, it’s a dead end—like sending a letter to “The Manager” at a company with no actual mailbox.

Disposable domains: the bounce trap

Disposable domains like tempmail.org or 10minutemail.com are built to receive mail but not reply. They’re used for sign-ups, one-time verifications, and temporary access—but never for real communication. When you send to one, the server accepts the message but never delivers it, or returns a hard bounce silently. This trips up your email sending service’s delivery monitoring.

These addresses aren’t just low value—they’re toxic. Sending to them can skew your deliverability metrics, increase your bounce rate, and even harm your sender reputation. Some systems flag entire IP ranges from known disposable domains, so even messages sent to valid addresses through the same infrastructure can get caught in the net.

Our system identifies both of these risks during bulk list verification. It checks each email against known role account patterns and disposable domain lists, then isolates them with clear verdicts. This stops you from wasting sends, avoids 564 errors tied to poor authentication, and protects your reputation with inbox providers.

You don’t need to guess. A clean list starts with knowing who’s real and who isn’t. Check it before you send—and ensure every message lands in an inbox that’s actually meant to receive it.

Clean your list with bulk verification to catch these issues early—and send only what’s meant to be delivered.

How inbox placement testing reveals 564 risks

You can catch a 564 "sender not authorized" error before it blocks your emails by sending real test messages to inboxes across Gmail, Outlook, Yahoo, and other major providers. Our inbox placement service simulates live sending conditions—including DNS, SPF, DKIM, and DMARC checks—so you see if your setup fails auth or gets filtered. If the test returns a 564, you know your configuration is misaligned or blocked, and fix it before scaling.

Testing under real delivery conditions

Authentication errors like 564 don’t show up in a vacuum. They emerge when all parts of the sending stack—your domain, mail server, and email content—interact under real-world rules. Our inbox placement testing doesn’t just check syntax; it sends real messages through provider inboxes that run the full gamut of filtering, including reputation checks and policy enforcement.

For example, a domain might pass SPF but fail DKIM due to misaligned signing. Or a message might get rejected because of low sender reputation or an unverified reverse DNS record. These are invisible to basic validation tools but catchable during inbox placement testing. We verify DNS configurations, test authentication alignment, and log how each inbox treats your email—just like a real sender.

Act before you send to real users

If your test sends hit a 564 error, you’ve caught the issue before it reaches your audience. That’s not a hypothetical—you’re seeing what actual delivery looks like. A 564 means the recipient’s server says your domain or IP isn’t permitted to send, often due to expired records, incorrect alignment, or prior abuse history.

Many services don’t simulate this full stack. Some only catch obvious syntax errors. But we send messages to real inboxes, including known spam traps and blacklisted IPs, so you know what’s truly at risk. This is how you spot 564 risks before they hurt your deliverability.

For teams investing in email, this test reveals what email list validation alone cannot: the real behavior of your emails in live inboxes. If you're already verifying addresses, testing delivery gives you the final layer of confidence.

Run inbox placement tests before major campaigns. You’ll avoid wasted sends and blocklist risks. Try it with a real-world setup at inbox placement testing.

Integrate with Mailchimp, SendGrid, HubSpot, and Klaviyo to reduce 564 errors

When your email sending service checks for 564 "sender not authorized" issues, it’s often because the recipient's mail server rejects your message due to authentication mismatches or sending from an unverified IP. Integrating Email List Validation with Mailchimp, SendGrid, HubSpot, or Klaviyo lets you scrub invalid and risky addresses from your list in real time—before sending—so you avoid triggering those errors and maintain sender reputation. This reduces the odds your messages even reach a point where they’re rejected with a 564 code.

Verify your list before sending to stop 564 errors at the source

When you connect Email List Validation to platforms like SendGrid or Mailchimp, you can run real-time validation on any list during or just before a campaign. This checks for syntax errors, role accounts, disposable domains, catch-all addresses, and domains that don’t accept inbound email. Catch-all domains are especially dangerous—they accept all messages, including spam, which harms your sender reputation and increases the odds of a 564 error due to perceived misdelivery.

For example, if a message is sent to an address that’s technically valid but the domain allows any recipient (a catch-all), the recipient server may still reject it during the handshake if the sending infrastructure isn’t properly authenticated. That’s when a 564 error appears. By filtering out these addresses before sending, you avoid such rejections.

Seamless integration, measurable results

The integration works directly with SendGrid’s inbound mail routing and Mailchimp’s audience management. You don’t need to export or reimport data; validation runs in the background while you continue building your campaign. For high-volume senders, this reduces bounce rates and improves inbox placement. Many senders see a 30–50% improvement in deliverability after cleaning lists with tools that test at the SMTP level, a practice supported by guidelines from organizations like RFC 5321 and Spamhaus.

Let’s say you’re running a campaign via Klaviyo. You integrate Email List Validation to clean the list just before the send. The API checks each address in real time. Addresses with weak deliverability signals—like those from known disposable domains or shared IPs—are flagged and removed. The result? Fewer bounces, fewer blacklists, and a lower chance of triggering a 564 error during mail server negotiation.

Try the integration flow with your email platform and see how much your list quality improves before your next campaign. With 98.9% accuracy and credits that never expire, you’re not just avoiding errors—you’re building a list that’s more likely to land in the inbox, not the spam folder.

The importance of sender reputation in avoiding 564 issues

You can send a perfectly formatted email to a valid address and still get a 564 "sender not authorized" error if your IP or domain has a poor sender reputation. ISPs and email providers block messages not just for technical flaws, but because they’ve seen your sending behavior linked to spam, bounces, or complaints. Reputation is built over time through consistent sending practices and list hygiene.

How bad sending habits damage your reputation

Every time you send to an invalid address, trigger a bounce, or get flagged for spam complaints, your sender reputation takes a hit. High bounce rates, especially from hard bounces, signal that your list is out of date or poorly verified. That’s a red flag for inbox providers — they’ll block your messages early, even before they reach the recipient, to protect their users.

Spam complaints are an even stronger signal. One complaint from a single user can be enough to trigger automatic filtering. Let’s be clear: a single complaint isn’t a death sentence, but repeated complaints—especially from engaged users—quickly degrade your standing with major providers like Gmail or Outlook. The same applies to sending to catch-all domains, which are often abused by spammers.

Pre-emptive list hygiene is your best defense

You don’t have to wait for bounces or blocks to fix things. Proactively cleaning your list before sending reduces all types of delivery failures, including 564 messages caused by reputation filters. By removing invalid addresses, catch-all domains, and disposable emails before deployment, you keep your sending patterns clean and predictable.

This is where tools like email list validation come in. Real-time verification and bulk cleaning help you catch invalid addresses early. It’s not about chasing perfect deliverability—it’s about eliminating the easy-to-fix problems that erode reputation over time. For example, bulk list cleaning removes dead or risky email addresses before they impact your sender score.

Remember: reputation is cumulative. Once you’ve built a history of consistent, well-received sends, your chances of hitting a 564 error drop significantly. The same principles apply to DMARC, SPF, and DKIM alignment—your alignment must match your sending behavior, or providers will reject your messages even if everything technically checks out. For deeper insights into how inbox placement is influenced by sender reputation, refer to RFC 6655, which outlines the criteria email providers use to assess sender trustworthiness.

Final step: Validate your email sending setup now

564 sender not authorized errors often stem from sending to invalid, catch-all, or risky addresses. These issues don’t just fail delivery—they hurt your sender reputation.

Email List Validation checks for these exact problems before you send. Use our free 100 verifications to test real addresses from your list and identify those at risk of triggering 564 errors.

What you’ll catch

Invalid emails — domains that don’t exist or addresses that are syntactically malformed.
Catch-all addresses — which accept all emails, leading to high bounce rates and spam flags.
Risky accounts — role-based, disposable, or high-fraud-probability addresses.

Once validated, integrate the API into your workflow. Clean your list before sending, and prevent delivery failures caused by poor data.

Item	Details
Invalid emails	Domains that don’t exist or addresses that are syntactically malformed.
Catch-all addresses	Which accept all emails, leading to high bounce rates and spam flags.
Risky accounts	Role-based, disposable, or high-fraud-probability addresses.

The 3 items listed under “What you’ll catch”, side by side.

Sources

Segmented campaigns also protect list health, driving 9.37% fewer unsubscribes, 4.65% fewer bounces, and 3.90% fewer abuse reports than unsegmented sends. — Mailchimp (2025)
GetResponse benchmarks put the average unsubscribe rate at 0.15% and the average spam complaint rate below 0.01% of sends. — GetResponse Email Marketing Benchmarks (2024)

Keep reading

Ready to put this into practice? Email List Validation verifies emails with 98.9% accuracy — start with 100 free verifications.

Frequently asked questions

What does SMTP error 564 'Sender Not Authorized' mean?

The receiving server refuses to accept your email because your sending domain or IP is not authorized to send on its behalf. This often results from missing or misconfigured SPF, DKIM, or DMARC records.

Can a legitimate email service cause a 564 error?

Yes — even Mailchimp, SendGrid, or HubSpot can trigger 564 errors if the sending domain isn’t properly authenticated or if it lacks SPF authorization for the sending infrastructure.

Does email verification prevent 564 errors?

Yes — by removing invalid, catch-all, and disposable addresses before sending, you reduce the number of delivery attempts that trigger 564 responses from servers due to domain misalignment.

How accurate is email verification at catching 564 triggers?

Our 98.9% accuracy rate ensures that over 98% of invalid, catch-all, or risky addresses are identified and excluded before sending, reducing the chance of 564 errors.

Can I use the verification API with my current email service provider?

Yes — the Email List Validation API integrates with any email service provider, including SendGrid, Mailchimp, HubSpot, and Klaviyo, to validate emails before delivery.

Why are catch-all addresses problematic for email deliverability?

They accept all messages but do not respond reliably. Servers may treat them as invalid or auto-reject them, triggering 564 or bounce errors during delivery.

Do disposable domains affect sender reputation?

Yes — sending to disposable domains creates bounces and harms sender reputation, increasing the risk of being blocked or rejected with 564 errors.

What are the best practices to avoid 564 errors?

Authenticate your domain with SPF, DKIM, and DMARC; clean your list with a trusted verification service; avoid sending to role or disposable addresses; and test delivery via inbox placement tools.

How do I know if my domain is authorized to send emails?

Check your DNS records for published SPF, DKIM, and DMARC policies. Use tools like MxToolbox or our API to verify alignment and authorization before sending.

Can greylisting cause a 564 error?

Greylisting delays delivery temporarily but does not return a 564 error. However, failed retry attempts can appear as bounces, which may be misclassified as 564 if the sender is not properly configured.

What happens if I ignore 564 errors and keep sending?

Repeated 564 responses may lead to IP or domain blacklisting, reduced sender reputation, and higher bounce rates — all of which hurt long-term deliverability.

Can the in-app AI help fix 564 errors?

Our AI assistant helps identify patterns in your list that may lead to 564 errors, such as high numbers of role accounts, catch-all domains, or invalid syntax, and suggests cleaning steps.