How to troubleshoot MX record issues with Cloudflare when one domain bounces?
Matthew Whittaker
Co-founder & CTO, Suped
Published 26 Jun 2025
Updated 16 Aug 2025
7 min read
Email bounces are incredibly frustrating. You send a critical message, only for it to come back with a cryptic error, especially when using a robust DNS provider like Cloudflare. When one domain bounces but others don't, it points to a specific configuration problem rather than a widespread issue. This can often be traced back to Mail Exchanger (MX) records, which are vital for directing incoming email to the correct server.
I've personally encountered situations where DNS lookups, like using dig, show one MX record, while the Cloudflare interface displays something entirely different. This discrepancy can lead to persistent bounces for specific recipients, even if most emails go through without a hitch. It's a classic example of a DNS anomaly that requires a targeted troubleshooting approach.
In this guide, I'll walk you through how to pinpoint and resolve these elusive MX record issues within Cloudflare when you're experiencing email bounces for just one domain. We'll cover everything from understanding the fundamentals of MX records to debugging complex DNS propagation challenges.
Understanding MX records and Cloudflare's role
MX records are a type of DNS record that specifies a mail server responsible for accepting email messages on behalf of a domain name. They act like a directory, telling sending mail servers where to deliver email for your domain. Each MX record includes a preference value, or priority, indicating the order in which mail servers should be tried, with lower numbers typically meaning higher priority.
When you use Cloudflare for your DNS, it becomes the authoritative source for your domain's records. While Cloudflare is excellent for speeding up websites and providing security, its proxying (the orange cloud) feature can interfere with mail traffic. For email to function correctly, any A records (or CNAMEs) associated with your mail server hostname (e.g., mail.yourdomain.com) should have the proxy status turned off (grey cloud), allowing mail traffic to bypass Cloudflare's network and go directly to your mail server.
If your mail server's A record is proxied, Cloudflare will attempt to route email traffic, which it is not designed to do, leading to delivery failures. This is a common pitfall that can cause email services to stop working. You can find more details on troubleshooting email issues with Cloudflare's DNS on their official documentation.
Important: Cloudflare proxying for email
When configuring Cloudflare DNS, ensure that any A records pointing to your mail server (e.g., mail.yourdomain.com) are set to DNS only (grey cloud icon). Activating Cloudflare's proxy for these records will prevent email from being delivered, as it will try to route mail through their HTTP proxy, which is not designed for SMTP traffic.
Common MX record misconfigurations
MX record issues often stem from simple misconfigurations. These can include typos in the hostname, incorrect priority values, or pointing to an outdated or incorrect mail server. In my experience, a particularly tricky scenario is when the MX record appears to be an auto-generated, unconventional hostname, like _dc-mx.e50ff5f0c784.example.org, which might work for most receivers but fail for one due to unique DNS resolution processes or strict policies on their end.
Another common issue is DNS propagation delays. After you update your MX records in Cloudflare, it can take some time for these changes to be reflected across the global DNS network. During this period, different DNS resolvers might still serve old, cached records, leading to inconsistent results. This explains why some domains receive emails fine, while others, relying on an un-updated cache, experience bounces. You should also understand how MX records impact sender reputation.
Furthermore, conflicts can arise if your domain's DNS is split between Cloudflare and another platform, such as a hosting provider's cPanel. Even if Cloudflare is the authoritative nameserver, an MX record might mistakenly persist on the old platform, causing confusion and routing errors. This is a common root cause of domain not configured MX host bounces.
Typical MX issues
Incorrect hostname: The mail server address listed in the MX record is misspelled or points to a non-existent host.
Wrong priority: Priority values are misconfigured, causing mail to be delivered to a backup server first or ignored altogether.
Outdated records: MX records were not updated after migrating mail servers or hosting providers.
Impact on email deliverability
Permanent bounces: Emails are returned with a 550 5.1.2 Host unknown error, indicating the sending server couldn't find a valid destination.
Inconsistent delivery: Some recipients receive emails, while others don't, due to varied DNS caching across the internet.
Reputation damage: Persistent bounces can negatively affect your sender reputation, increasing the likelihood of future emails landing in spam folders or being blocklisted (blacklisted).
Diagnosing the bounce: a step-by-step approach
The first step in troubleshooting is to analyze the bounce message. It often contains clues, such as SMTP error codes like 550 5.1.2 Host unknown. This specific error indicates that the receiving mail server could not resolve your domain's MX record or the hostname specified within it. It might also show the problematic MX record explicitly, providing a direct lead.
Next, use command-line tools like dig (on Linux/macOS) or nslookup (on Windows) to query your domain's MX records. It's also helpful to use online DNS checking tools that perform lookups from various locations, giving you a global view of propagation. Compare the output of these tools with what you have configured in your Cloudflare DNS settings. Discrepancies here are a strong indicator of the problem.
Pay close attention to the authoritative nameservers for your domain. Use dig +trace or whois to confirm that Cloudflare is indeed listed as the nameserver. If you find an MX record in the bounce that doesn't correspond to any record in Cloudflare, or if Cloudflare is showing a different MX record than what external tools report, you've likely identified the problem area. This kind of problem requires a thorough email bounce troubleshooting process.
Addressing the authoritative server and propagation
If your Cloudflare nameservers are indeed authoritative, but they are refusing to answer MX queries for your domain (showing a REFUSED status in dig queries to them), this is a critical issue. This essentially means Cloudflare isn't properly serving your MX records, leading to 'domain does not exist' or 'invalid sender domain' errors for some recipients. You can verify this by using a non-caching resolver tool like Word to the Wise's DNS tool.
This usually points to an underlying configuration problem within Cloudflare itself, or a conflict with an external DNS provider still attempting to manage your MX records. Even if other mail flows, the specific recipient domain that's bouncing might be querying an NXDOMAIN (non-existent domain) for your mail server, or it's receiving a refusal from your authoritative DNS.
The solution involves meticulously verifying your MX records within your Cloudflare dashboard and ensuring no conflicting records exist elsewhere. Delete any old, incorrect, or auto-generated MX entries that are causing issues and add the correct ones precisely as required by your mail provider. Remember that DNS propagation can take up to 48 hours, though Cloudflare changes often apply much faster. Continuous verification using external tools is key until all resolvers show the correct records.
Resolving persistent MX record issues
Review all DNS records: In your Cloudflare dashboard, carefully inspect all MX records for your domain. Delete any that are incorrect or redundant. Ensure no legacy MX records from previous providers remain.
Add correct MX records: Input the precise MX records provided by your current email service provider, including their correct priority values. Double-check for typos.
Verify A records for mail hostnames: Make sure any A records (e.g., mail.yourdomain.com) used in your MX records are set to 'DNS only' (grey cloud) in Cloudflare.
Monitor propagation: Use global DNS propagation checkers to ensure your changes are visible worldwide. Be patient, as it can take time for all DNS servers to update.
Views from the trenches
Best practices
Regularly verify your MX records across multiple DNS lookup tools to confirm consistent propagation.
Always ensure your mail-related A records are unproxied (grey cloud) in Cloudflare to prevent email routing issues.
Use bounce messages as diagnostic tools; the error codes and host information are crucial for pinpointing problems.
Common pitfalls
Typographical errors or outdated MX record entries can lead to intermittent email delivery problems.
Conflicting DNS configurations between Cloudflare and other control panels, like cPanel, can cause records not to update correctly.
Assuming immediate propagation of DNS changes, as caching on various DNS servers can cause delays.
Expert tips
When troubleshooting, query the authoritative nameservers directly to bypass caching issues.
If only one domain is bouncing, investigate its specific DNS resolution path compared to domains that are receiving emails successfully.
Be persistent in verifying that the correct MX records are recognized by all major DNS resolvers after making changes.
Expert view
Expert from Email Geeks says: Sometimes a cached bad MX record can linger, causing different DNS servers to return varying results even after a fix.
2021-12-16 - Email Geeks
Expert view
Expert from Email Geeks says: If DNS tools show varying results but the authoritative server is correct, it usually indicates a waiting game for caching to expire.
2021-12-16 - Email Geeks
Key takeaways for robust email delivery
Troubleshooting MX record issues with Cloudflare can be complex, especially when only one domain is affected. The key is a systematic approach: scrutinize bounce messages, use robust DNS lookup tools, understand the difference between local and authoritative DNS results, and ensure Cloudflare's proxy settings are correctly configured for mail. With patience and persistence, you can ensure your email deliverability remains consistent and reliable across all your domains.
Cloudflare. When one domain bounces but others don't, it points to a specific configuration problem rather than a widespread issue. This can often be traced back to Mail Exchanger (MX) records, which are vital for directing incoming email to the correct server.
DNS propagation can take up to 48 hours, though 
