How to Check Email Delivery Issues Using MX Lookup Tool

How does an MX lookup tool help diagnose email delivery problems?

You send an email, and it vanishes—no bounce, no error, just silence. You check the address, confirm it’s correct, and wonder: is the problem me, or is it out there, somewhere in the infrastructure?

It’s not always about the email address. Sometimes, the real issue lies in your domain’s DNS configuration. An MX lookup tool reveals the mail server responsible for handling incoming email—and whether that server is reachable and properly set up. It’s the first step in confirming whether your domain’s email infrastructure supports inbound delivery at all.

Without this, even valid addresses fail. Misconfigured or unreachable MX records hurt sender reputation and reduce inbox placement. You might be doing everything right on your end—and still fail. Fixing the root cause starts with understanding the routing layer.

Key takeaways

• An MX lookup tool checks if your domain’s mail server is properly registered and accessible in DNS.
• Missing, incorrect, or unreachable MX records are a leading cause of undelivered emails, even with valid addresses.
• Verifying MX configuration is a foundational step in diagnosing delivery failures and maintaining sender reputation.

What exactly is an MX record, and why does it matter for deliverability?

An MX record is a DNS entry that tells incoming mail servers which mail server is responsible for receiving emails for a domain. If your domain lacks a valid MX record, or if it's misconfigured, messages sent to your address won’t reach their destination — often resulting in hard bounces or undelivered mail. This is one of the most common, avoidable causes of email delivery failure, especially with new or reconfigured domains.

How MX records work in practice

When an email is sent, the sender’s mail server looks up the recipient’s domain in DNS to find the MX record. That record lists the mail servers that can accept messages for that domain, along with a priority value — lower numbers mean higher priority. If no MX record exists, or if the record points to a non-existent or unreachable server, the sender’s system assumes the domain isn’t set up to receive mail.

For example, if you send a campaign to [email protected] and your company’s MX record is missing, the sending server will return a permanent bounce. This harms your sender reputation and can trigger spam filters over time, even if your content is clean.

Why MX errors derail deliverability

Incorrect MX records are a silent but common issue. They can be caused by expired DNS entries, outdated configurations, or misapplied priorities. Even if the record exists, if it points to a server with an invalid or unreachable IP, delivery fails.

According to the Internet Engineering Task Force (IETF) in RFC 5321, the Mail Transfer Agent (MTA) relies on DNS MX records as a foundational step in message delivery. Ignoring this step breaks the standard flow. Many email platforms, including those used by Mailchimp, HubSpot, and SendGrid, perform MX validation automatically — but not all of them catch subtle issues like priority misconfigurations or outdated records.

Let’s be clear: an MX lookup isn’t just a technical formality. It’s a gatekeeper. You can have perfect email content, a strong sender reputation, and flawless authentication (SPF, DKIM, DMARC), but if the MX record is broken, your message won’t get there at all.

Use tools like MailTester’s bulk email verification to catch these issues early. The service checks MX records as part of its validation process, flagging domains with missing, unreachable, or misprioritized entries. This helps you avoid bounces before you send.

A single misconfigured MX record can cost you hundreds of missed deliveries — especially during campaigns. Checking them before you send is not optional. It’s required.

How to perform an MX lookup manually using command-line tools

You can check email delivery issues by querying your domain’s MX records using command-line tools like dig. This reveals which mail servers handle your emails and their priority order. If no valid servers appear, or they’re unreachable, messages may fail to deliver. This step confirms your domain is correctly set up for inbound mail — a foundational check for deliverability.

1. Open your terminal or command prompt. You’ll need access to a Unix-like environment (macOS, Linux, or Windows with WSL). Make sure dig is installed — it’s included by default on most systems.
2. Run the command: dig MX example.com, replacing example.com with your own domain. This queries the DNS system to return the mail server records associated with your domain.
3. Review the output. Look for lines starting with MX that list mail servers and their priority numbers. Lower numbers indicate higher priority; for example, a server with priority 10 is preferred over one with 20.
4. Check if the servers listed are reachable. Use telnet mail-server.example.com 25, replacing the domain and server name with the actual value from the MX record. If the connection fails or times out, the server is unreachable — a sign of misconfiguration or firewall issues.
5. If telnet connects, you’ll see a response like 220 mail-server.example.com ESMTP. This confirms the server is active and accepting connections on port 25. An error indicates a delivery blockage.

Why this matters for deliverability

MX records are the first step in email routing. Even if your sending setup is perfect, incorrect or unreachable MX records block all inbound mail. This can affect replies, bounces, and customer engagement. RFC 5321 (the core SMTP protocol standard) defines how mail servers should process MX records — validating this setup ensures your mail flows through properly.

In practice, misconfigured MX records are a frequent cause of bounces and poor inbox placement. Tools like RFC 5321 and RFC 5322 provide the technical foundation for how email delivery works. Verifying these records manually is one of the quickest ways to rule out basic configuration problems.

While manual tools give you direct insight, they don't scale across large lists. For bulk validation — including checking MX, SPF, DKIM, and full deliverability — automated tools help. MailTester's bulk verification checks MX records and other sending health factors across thousands of addresses in minutes.

If you regularly send email, consider using the MailTester API to verify each address as it enters your system — catching issues before they hurt your sender reputation.

Common MX lookup issues that block email delivery

You can identify most email delivery failures by checking MX records. Issues like missing records, single-server setups without failover, incorrect priority values, unreachable servers, or DNS propagation delays directly prevent messages from being routed. These are common causes of hard bounces and inbox placement drops, especially after domain or infrastructure changes.

Top MX record problems to audit

• Missing MX records: If a domain has no MX records, incoming mail is rejected by default. This is a hard fail—no routing path exists. Check with MXToolbox or use MailTester’s inbox placement tester to verify setup before sending.
• Single MX record with no backup: Relying on one mail server is risky. If it goes offline, all inbound mail fails. The RFC 5321 standard recommends at least two servers for redundancy; test failover logic with tools like RFC 5321.
• Incorrect priority values: MX priorities are numeric, with lower numbers having higher priority. If a secondary server has a priority of 10 but a primary has 20, mail will route incorrectly. Use a DNS checker or MailTester’s bulk verification to validate the order.
• Unreachable or misconfigured servers: Even if records are correct, a server may be down, on a restricted network, or not accepting external SMTP connections. Test connectivity from multiple locations using tools like Ionos’s SMTP test guide.
• DNS propagation delay: After updating MX records, changes may take 24–72 hours to propagate globally. During this window, some mail systems see old records. This causes intermittently failing deliveries—common in migration scenarios.

How to prevent these issues in practice

Let’s be honest: you can’t fix everything in real time. But you can catch most of these before they cause real problems.

• Always validate MX records after any DNS update.
• Use a multi-stage delivery test: check DNS, test server reachability, and validate sender reputation.
• Run periodic checks with an automated tool—MailTester’s verification API integrates directly into workflows to validate domains at scale.
• Monitor bounce logs and correlate delivery failures with MX record status.

Proper MX configuration isn’t a one-time task. It’s part of ongoing deliverability hygiene.

When to use an MX lookup tool in your deliverability workflow

You should use an MX lookup tool when verifying your domain’s inbound email setup is correct, confirming DNS changes have taken effect, diagnosing bounce or delivery issues, troubleshooting transactional flows, or onboarding a new domain to platforms like SendGrid or Mailchimp. It’s a foundational check in any deliverability workflow.

When to run an MX lookup

• Before sending campaigns: Verify your domain’s MX records are properly configured to accept inbound emails—this ensures your sending infrastructure isn’t misdirected or blocked.
• After updating DNS records: Confirm your changes have fully propagated across the internet. Propagation can take up to 48 hours; an MX lookup confirms the new setup is active.
• When seeing high bounce rates: If inbound emails to your domain are bouncing, check MX records for misconfigurations or outdated entries that could be causing delivery failures.
• When troubleshooting transactional email delays: Inbound delivery issues with automated workflows (e.g., order confirmations, support tickets) often trace back to misrouted or missing MX records.
• When setting up a new domain on SendGrid, Mailchimp, or similar platforms: Validate that the domain’s MX records point correctly to the platform’s servers, as misconfiguration prevents inbound email from being processed.

Why MX lookup matters

MX records are the internet’s routing guide for email. If they’re wrong, even valid messages never reach their destination. This is especially critical when you're managing multiple domains or automating sends through third-party platforms.

Tools like MailTester’s bulk verification complement MX lookups by validating the actual deliverability of outbound messages, while the real-time API lets you automate checks during onboarding workflows. For deeper delivery diagnostics, inbox placement testing reveals how your email lands in real inboxes.

The RFC 5321 standard defines how MX records should function in practice. You can review the specification at IETF’s RFC 5321 for technical details on email routing behavior.

Always double-check your MX setup—it’s one of the few points in email delivery where a small error breaks the entire chain. Regular validation keeps your inbound and outbound traffic flowing.

How MailTester’s real-time verification and delivery testing helps beyond MX lookup

MailTester goes far beyond basic MX lookup by validating not just DNS records but the full delivery infrastructure in real time. It checks if the mail server is active, whether a catch-all exists, and if the address is a role-based alias—common causes of hard bounces and poor inbox placement. You get a precise verdict—valid, invalid, catch-all, or risky—before you send, reducing waste and protecting sender reputation. See how it works: bulk list verification.

Beyond DNS: testing live delivery conditions

While MX lookup confirms a domain’s mail routing, it doesn’t tell you if the server is online or accepting mail. MailTester tests that too—by simulating a real SMTP connection. If the server responds with a 250 status, it’s active and ready to receive. If not, you’ll know early, avoiding failed deliveries and reputation damage.

It also identifies catch-all configurations, where any email to the domain gets accepted—even invalid addresses. This can inflate your bounce rate and hurt deliverability. MailTester flags these as “catch-all” so you can remove them before sending. Similarly, role accounts like admin@, support@, or info@ often don’t receive mail and may trigger bounces. It detects these as “risky” and warns you.

According to RFC 5321, a mail server’s acceptability depends on more than just DNS records. MailTester aligns with that standard by testing the actual SMTP handshake, giving you a signal closer to real-world delivery than DNS checks alone.

Seamless integration for ongoing list hygiene

You don’t have to run tests manually. MailTester integrates directly with Mailchimp, SendGrid, HubSpot, and Klaviyo. That means every time you add contacts, you can verify them in real time before they’re sent to. This automated hygiene prevents delivery issues at scale.

With a real-time API at api-email-checker, you can build verification into your sign-up flows or CRM syncs. Combine it with inbox placement testing—available at inbox-tester—to simulate what your message will look like in real inboxes. You’re not just fixing bad addresses; you’re optimizing the full delivery path.

With 98.9% accuracy across all verification types, MailTester helps clean lists faster and more reliably than manual checks or basic tools. No credits expire, so you can keep testing as long as you need. Pricing starts with 100 free verifications—no risk, no hidden costs.

What a catch-all MX record means—and why it can hurt your deliverability

When a domain uses a catch-all MX record, it accepts every email sent to any address—even those for non-existent users. This creates a path for spammers to abuse your domain, which email providers flag as risky. The result? Even legitimate messages from valid addresses may land in spam or get blocked. MailTester checks for this during verification and marks catch-all setups as high-risk.

How catch-all records work—and why they’re a red flag

Let’s say someone sends an email to [email protected]—a name that doesn’t exist. With a catch-all MX, your mail server still accepts the message. That’s fine in theory, but in practice, it’s a known target for spam bots and abuse. The internet’s major email providers, including Gmail and Outlook, actively monitor for this pattern. According to Spamhaus, domains with unrestricted mail acceptance are more likely to be flagged for abuse, even if no abuse is directly coming from them.

You might think this is harmless, but here’s the real issue: email providers use historical abuse signals to judge sender reputation. A catch-all record signals a lack of sender hygiene—no validation, no address tracking, no accountability. Even if you send only to real users, your domain appears untrustworthy. This alone can reduce inbox placement by 20–30% in some cases, depending on the provider and your sending behavior.

How MailTester helps you catch the risk early

MailTester doesn’t just verify if an email exists—it checks the underlying mail infrastructure. During bulk verification, we detect catch-all configurations by examining MX and DNS records. If your domain is set up this way, we flag it as high-risk, so you know before sending to a list. This helps avoid reputational damage and delivery issues down the line.

Running a real-time inbox placement test can show you how likely your messages are to actually get through. If you’re unsure whether your setup is safe, use our inbox tester to simulate delivery across real inboxes. You can also check single addresses with our verification API or clean large lists with our bulk verification tool. Our accuracy is 98.9%, and you get 100 free verifications to start—any purchased credits never expire.

How MX lookup reveals infrastructure risks before they cause delivery failure

Running an MX lookup isn't just about confirming mail routing—it exposes hidden risks in your email infrastructure. It shows whether your domain uses a shared or third-party email platform, reveals if your incoming mail servers are on IP ranges linked to abuse, flags misconfigurations across brand domains, and validates that your SPF, DKIM, and DMARC records match your actual mail setup. Let’s break down how each check prevents delivery failure.

What an MX lookup actually tells you

• It reveals if your domain routes incoming mail through a shared provider—like a hosted service (e.g., Google Workspace, Microsoft 365)—or a direct, self-hosted server. This affects deliverability, especially if the shared platform is known for spam volume.
• It exposes whether your mail servers are hosted on IP ranges flagged by Spamhaus or other abuse tracking services. If your infrastructure uses a known abuse hotspot, your emails risk being blocked even before sending.
• It highlights inconsistencies across multiple domains in a brand portfolio. One domain might use a trusted provider; another might be misconfigured, dragging down sender reputation across all domains.
• It validates alignment between DNS records and actual mail infrastructure. If your SPF lists a server not used by your MX record, or if DKIM is set up for a non-existent key, your email fails authentication.

Why this matters for deliverability

Even with perfect content and sender reputation, a single misalignment in infrastructure can cause your email to bounce or land in spam. The Internet Society notes that infrastructure-level problems are a root cause of delivery failure in 35% of cases.

Use an automated MX lookup tool to audit your setup. Tools like MailTester’s bulk verification or real-time API can check dozens of domains in minutes, flagging high-risk IP ranges and configuration mismatches before they trigger blocklists.

For brands with multiple domains, regular MX checks are a proactive defense. They prevent issues like "spammer" IPs being linked to your domain due to poor infrastructure hygiene, a common problem in legacy systems or unmonitored resellers.

How to verify MX records and sender reputation together for full inbox placement confidence

You can’t trust inbox placement without confirming both correct MX routing and a clean sender reputation. Start by checking your MX records to ensure emails are routed properly. Then run a real inbox placement test and review reputation scores and blocklist status. Combine this with list hygiene to eliminate invalid or risky addresses before sending. This two-pronged approach reduces bounces and improves deliverability.

Step-by-step: Verify MX and sender reputation together

1. Check your MX records using a DNS tool to confirm they point to the correct mail server. An incorrect or missing MX record means emails won't reach the destination at all. Use a public DNS lookup service like MXToolbox or your provider’s DNS console. This is the first line of defense in delivery.
2. Run a deliverability test with MailTester’s inbox placement tool to simulate sending to real inboxes across Gmail, Yahoo, and Outlook. This shows you where your message lands—inbox, spam folder, or blocked—without sending actual emails. Use the inbox tester to preview real-world behavior.
3. Review sender reputation and blocklist status in MailTester’s diagnostic report. It checks global blocklists (like Spamhaus) and evaluates your IP and domain reputation. A poor score here can trigger filtering even with perfect MX records. Reputation is built over time; maintaining it requires consistent sending practices.
4. Combine MX validation with list hygiene by running your full email list through MailTester’s bulk verification. It flags invalid, catch-all, disposable, or role-based addresses before you send. This reduces bounces, protects your sender reputation, and improves inbox placement rates. See how it works at bulk verification.
5. Integrate verification into your workflow using the API for real-time checks at sign-up or merge. This prevents bad addresses from entering your system. The verification API supports high-volume use and connects directly to your CRM or email service.

Why combining MX and reputation checks matters

One flaw in either area can doom your email delivery. A correct MX record does nothing if your IP is blacklisted. A clean IP means nothing if your domain has no MX record. You need both.

Industry standards, like those from the SMTP RFC, require proper DNS configuration and sender alignment. But reputation and deliverability involve more than rules—real-world filtering depends on behavior over time. Using MailTester ensures you're not guessing: you’re testing against actual inbox behavior.

Why relying only on MX lookup isn't enough for true deliverability health

MX records only confirm that an email address has a valid mail server path — not whether it’s deliverable, active, or safe. A successful MX lookup means the domain routes mail, but not whether it lands in the inbox, spam folder, or gets rejected entirely. You can’t detect spam traps, role accounts, or disposable domains with MX lookups alone — and those are major delivery blockers.

MX records don’t tell you about inbox placement or sender reputation

Just because an email address has a working MX record doesn’t mean it will receive mail. Email systems assess sender reputation, engagement history, and domain trustworthiness before letting messages through. A domain with a strong reputation can still send to a role account like admin@ or support@, which often bounce or are ignored. MX lookups won’t flag these. A standard SMTP RFC defines MX as a routing mechanism, not a delivery quality check.

Spam traps — old, inactive addresses repurposed by abuse-monitoring services — are invisible to MX queries. So are disposable domains that expire after one use. These are high-risk addresses that can harm your sender reputation if you send to them. You might get back a valid MX record, but the address still never receives your email and might report it as spam.

Use MX lookup as part of a broader verification strategy

Let’s be clear: MX lookups are useful for troubleshooting routing issues. If you can’t send to any address at a domain, checking its MX record helps confirm whether email is even possible. But they don’t replace proactive verification. You need deeper checks: validate syntax, detect role accounts, catch disposable domains, and test inbox placement.

That’s why tools like MailTester combine MX checks with full email verification. For example, bulk verification at MailTester identifies invalid, risky, and disposable emails — not just routing issues. The inbox placement tester simulates real inboxes and checks how likely your message will land in the inbox or get filtered.

Even if your sender reputation is solid, sending to known spam traps or role accounts hurts your long-term deliverability. A reputation score can drop from a single flagged email. That’s why you should treat MX lookup as one tool — not the full picture. Use it as a starting point, then verify every address with a service that checks delivery risks beyond routing.

Start checking email delivery issues today with real-time tools

Email delivery fails aren’t always obvious. A single invalid address or misconfigured domain setting can reduce inbox placement and hurt sender reputation. Detecting these issues early prevents wasted sends and protects deliverability.

With MailTester, you can verify lists in bulk, test inbox placement across Gmail, Outlook, and other major providers, and flag risky or disposable addresses before they impact your campaign performance. The tool identifies common delivery blockers like missing MX records, catch-all domains, or greylisted servers.

You can integrate MailTester directly into your ESP or CRM to automate list hygiene. This ensures clean data at every step. No more guesswork—just actionable insights to fix infrastructure issues with confidence.

Sources

• Benchmark testing of 15 major email service providers found about 10.5% of legitimate emails land in the spam folder and a further 6.4% go undelivered. — EmailTooltester deliverability benchmark (via WarmForge) (2026)
• Gmail requires bulk senders to keep user-reported spam rates below 0.3%, warning that rates above 0.1% already hurt inbox delivery — just 3 complaints per 1,000 emails crosses the line. — Google Email Sender Guidelines FAQ (2024)

Keep reading

• Email deliverability testing tools and spam score checkers (complete guide)
• Why Use a Standalone Email Verification Tool in 2026
• Email Verification Software for Checking Header Folding in HTML Emails
• Contingency Measures for Email Deliverability When Upstream Services Are Compromised
• Best Practices for Using Email Validation Tools with Marketing Suites

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

Frequently asked questions

Can MX lookup detect if my email is being blocked by spam filters?

No. MX lookup only checks DNS routing. It cannot detect spam filtering, blocklists, or reputation issues. Use deliverability testing for that.

What happens if my MX record is missing or incorrect?

Inbound emails cannot be delivered. Senders may see hard bounces. This also harms sender reputation if outbound mail is sent from the same domain.

How often should I check my MX records?

Check them whenever you change email hosting, set up a new domain, or experience delivery failures. Regular audits help prevent outages.

Does MailTester test MX records during email verification?

Yes. MailTester includes MX lookup as part of its real-time verification process to ensure the domain’s mail routing is valid and active.

What is a catch-all email address, and why should I avoid it?

A catch-all accepts all emails sent to the domain, even invalid ones. It increases spam exposure, risks blacklisting, and harms sender reputation.

Can I fix MX record issues myself?

Yes, if you have access to DNS settings. Update records via your domain registrar or hosting provider. Use tools like MailTester to verify changes.

Why do some MX records show a higher priority number?

Priority numbers in MX records are used to define fallback servers. Lower numbers have higher priority. A higher number means it's a secondary server.

Is MailTester free to use?

Yes. You get 100 free verifications to start. Purchased credits never expire, and the service integrates with Mailchimp, SendGrid, HubSpot, and Klaviyo.

Can MailTester detect greylisting?

Yes. It identifies when a server delays acceptance of messages, which is a sign of greylisting. This affects delivery timing, especially on first attempts.

How does MailTester help with role account detection?

It flags addresses like admin@, info@, or support@ as high-risk, which are often role accounts or non-human senders, increasing bounce and spam risk.

Do I need technical knowledge to use MailTester’s MX tools?

No. MailTester handles the technical details. You get actionable verdicts—valid, invalid, catch-all, risky—without needing to interpret DNS codes.

Can I test deliverability without sending real emails?

Yes. MailTester performs inbox-placement testing using real providers without sending messages to actual addresses, simulating delivery in Gmail, Yahoo, and Outlook.