Why are emails bouncing with 'domain does not exist' or 'invalid sender domain' errors?
Matthew Whittaker
Co-founder & CTO, Suped
Published 31 Jul 2025
Updated 19 Aug 2025
7 min read
Encountering email bounce messages like "domain does not exist" or "invalid sender domain" can be frustrating. These messages indicate that the recipient's mail server cannot validate the sender's domain, leading to email rejection. Such bounces are distinct from a user unknown bounce which typically points to an issue with the recipient's specific email address. Instead, these errors signal a deeper problem with the domain itself or its configuration within the Domain Name System (DNS).
When your emails return with these particular bounce errors, it often suggests that the receiving server couldn't locate or verify the sending domain. This can be due to various reasons, from simple typos to complex DNS record misconfigurations. Understanding the root cause is crucial for restoring your email deliverability and ensuring your messages reach their intended recipients.
Understanding the bounce errors
When you encounter a bounce message stating "domain does not exist," it means the receiving mail server attempted to perform a DNS lookup for the sender's domain and failed to find any record of it. This essentially tells the server that the domain specified in the sender's email address simply isn't registered or isn't resolvable on the internet. It's like trying to call a phone number that doesn't exist.
The "invalid sender domain" error, while similar, often implies that the domain exists but lacks proper configuration or authentication. The recipient's server might be able to find the domain's DNS records, but it then determines that something about the setup, such as SPF, DKIM, or DMARC, is incorrect or missing, leading to the rejection of the email. Both of these are hard bounces, meaning the email is permanently undeliverable to that address.
These errors directly impact your sender reputation. A high volume of such bounces signals to internet service providers (ISPs) that your sending practices might be problematic, potentially leading to your emails being marked as spam or your domain (or IP address) ending up on a blacklist. Here's an example of a common bounce message you might see:
Example bounce messageplaintext
failed,5.1.8 (bad sender's system address),smtp;553 5.1.8 <delivery@yourdomain.com>... Domain of sender address delivery@yourdomain.com does not exist
Another common variant of this bounce involves the 550 SMTP error code, often seen as "550 5.1.0 Invalid sender domain".
Common causes of these bounce errors
These errors frequently stem from issues with how your domain's DNS records are configured. DNS records are like the internet's phonebook, directing traffic for your domain. If your Mail Exchange (MX) records, which specify your mail servers, are missing, incorrect, or pointing to a non-existent host, mail servers won't be able to route mail for your domain. Similarly, problems with A records or name servers can prevent the domain itself from being resolved.
Email authentication records, specifically SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance), play a critical role. If these records are misconfigured or absent, receiving servers may reject your emails because they cannot verify that the email truly originated from your domain. For instance, an SPF record might incorrectly list authorized sending servers, or a DKIM signature might not align, leading to an "invalid sender domain" response.
A less common but significant cause is domain expiration. If your domain name registration lapses, the domain effectively "does not exist" on the internet. While typically caught and renewed, even a temporary lapse can cause widespread bounce issues. Additionally, if your sending IP address or domain is on an email blacklist (or blocklist), some recipient servers may respond with domain-related errors as a security measure.
Finally, a simple typo in the sender's email address within your email sending system, or even within the recipient's address itself (though less likely for "domain does not exist" errors), can trigger these bounces. It's always worth double-checking the exact address that is bouncing.
Valid DNS configuration
MX records: Correctly point to your mail servers (e.g., google.com, microsoft.com for Exchange Online).
SPF record: Includes all authorized sending IPs and domains with a correct policy (e.g., ~all or -all).
DKIM records: Proper CNAME or TXT records for all selectors, correctly publishing public keys.
Missing MX records: No mail servers found, leading to "domain does not exist" errors for mail flow.
Incorrect SPF record: Not including all sending sources or having syntax errors, causing "invalid sender domain" rejections.
Invalid DKIM keys: DNS records not matching the signing key used by the sender, leading to authentication failures.
Domain expiration: Domain becomes unresolvable, resulting in a "domain does not exist" bounce.
Diagnosing the problem
The first step in resolving these bounces is to systematically diagnose the issue. Begin by reviewing the exact bounce message or non-delivery report (NDR). These messages often contain specific SMTP error codes (like 5.1.8 or 5.1.0) and descriptive text that can pinpoint whether the problem lies with the domain's existence or its authentication. Look for phrases such as "Domain of sender address does not exist" or "Invalid sender domain."
Critical DNS checks
MX records: Verify they are present and correctly configured. An absent or misconfigured MX record is a primary cause of domain does not exist type bounces for your own sending domain.
A record: Ensure your domain has a valid A record pointing to your website's IP address. While not directly related to email routing, a missing A record can indicate broader DNS problems.
SPF and DKIM: Use an email deliverability tester to check the validity and syntax of your SPF and DKIM records. Even small errors can lead to authentication failures.
DMARC reports: If you have DMARC enabled, regularly review your DMARC reports. These reports provide insights into authentication failures, including why your domain might be perceived as invalid by receiving servers. Pay attention to the 5.1.8 error code.
Domain registration: Confirm that your domain registration is active and has not expired. A domain expiration can instantly lead to domain does not exist bounces.
If your domain or IP is on a blacklist or blocklist, this can also trigger invalid sender domain errors, as receiving servers may simply reject mail from identified spam sources. Use a blocklist checker to see if your domain or IP is listed. Once you have identified the specific error and potential cause, you can proceed with the appropriate solution.
SMTP error code
Description
Likely cause
550 5.1.8
Bad sender's system address. Domain of sender address does not exist.
Sender domain DNS lookup failure, or domain expired. Can also indicate a temporary DNS issue.
550 5.1.0
Invalid sender domain.
Domain exists but fails authentication (SPF, DKIM, DMARC) or is on a blocklist. Sometimes a typo.
450 DNS lookup fail
Temporary DNS failure for the sender's domain.
Intermittent DNS issue, potentially temporary. Check MX records.
Solutions and prevention
The most direct solution for "domain does not exist" errors is to correct any DNS issues. Ensure your domain's MX records are properly configured and pointing to the correct mail servers. Use a DNS lookup tool to verify that your MX, A, and name server records are resolvable and correct. If your domain has expired, renew it immediately through your domain registrar.
For "invalid sender domain" issues, focus on your email authentication. Double-check your SPF record to ensure it includes all legitimate sending IP addresses and domains. Your DKIM records should be correctly published in your DNS and align with the signing practices of your email service provider. Remember that SPF can fail due to DNS lookup limits, so keep it concise.
DMARC implementation
Implementing or refining your DMARC policy is critical. DMARC relies on SPF and DKIM for alignment. If either fails to align, DMARC can instruct the receiving server to reject or quarantine the email. Start with a relaxed policy (p=none) to monitor bounce rates and authentication issues before moving to quarantine or reject policies. DMARC reports (RUA and RUF) will provide invaluable data on why your emails are bouncing with these errors.
Regularly monitoring your domain's health and email sending performance is key to prevention. Use a blocklist monitoring service to quickly detect if your IP or domain gets listed on a blacklist (or blocklist). Additionally, ensure your email lists are clean and regularly validated to avoid sending to non-existent domains or invalid addresses, which can otherwise contribute to poor sender reputation.
Views from the trenches
Best practices
Maintain meticulous DNS records for your domain, double-checking MX, SPF, DKIM, and DMARC settings regularly.
Set up DMARC monitoring and alerts to quickly identify authentication failures and misconfigurations.
Monitor domain expiration dates diligently to prevent unexpected service interruptions and bounces.
Use an email verification service to clean your email lists and remove invalid or non-existent domains before sending.
Common pitfalls
Overlooking subtle typos in DNS entries or email addresses that can cause validation failures.
Assuming DNS records are correctly set up after a domain transfer or platform migration without verification.
Ignoring DMARC reports, which contain critical insights into domain authentication failures.
Failing to renew domain registration, leading to severe and immediate email deliverability issues.
Expert tips
Always test your email setup after making any changes to DNS or email sending configurations. This can help catch issues before they impact your live campaigns.
Implement a DMARC policy with reporting (p=none) initially to gather data without affecting delivery, then gradually move to stricter policies.
Regularly check major blocklists (blacklists) to ensure your domain and IP addresses are not listed, as this can lead to 'invalid sender domain' rejections.
Automate domain and DNS monitoring where possible to receive proactive alerts about any critical changes or potential issues.
Expert view
Expert from Email Geeks says they often see this error when the MX record for the return-path domain is missing or misconfigured. It's usually the first thing to check.
2019-10-03 - Email Geeks
Marketer view
Marketer from Email Geeks says they've observed these bounces occurring when a domain's registration lapses. Even if quickly renewed, the temporary lapse can trigger a surge of these errors.
2019-10-03 - Email Geeks
Maintaining a healthy sender reputation
Email bounces with "domain does not exist" or "invalid sender domain" messages are clear indicators of fundamental issues with your domain's DNS configuration or authentication. Ignoring these warnings can severely damage your sender reputation and impact your overall email deliverability. Maintaining a healthy domain and robust authentication practices are cornerstones of successful email communication.
By proactively addressing DNS configurations, correctly setting up SPF, DKIM, and DMARC, and regularly monitoring your domain for potential issues or blocklist (or blacklist) placements, you can significantly reduce bounce rates and ensure your emails consistently reach the inbox. A strong foundation in these technical areas is essential for any sender looking to achieve high deliverability rates.
google.com, 
microsoft.com for Exchange Online).
