MX (Mail Exchange) records are the DNS records that tell the internet where to deliver email for your domain. If your MX records are missing, misconfigured, or pointing to the wrong servers, incoming mail will bounce or disappear entirely. Our free MX record lookup tool queries any domain's MX configuration, displays the results with priority values, and validates that each mail server is reachable.
What Are MX Records?
An MX record is a DNS resource record defined in RFC 5321 and RFC 1035 that specifies the mail server responsible for accepting email on behalf of a domain. Each MX record contains two pieces of information: a priority value (also called preference) and a hostname.
When someone sends an email to [email protected], the sending mail server queries DNS for the MX records of example.com. It then attempts delivery to the server with the lowest priority number first. If that server is unavailable, it falls back to the next-lowest priority, and so on. This mechanism provides built-in redundancy for mail delivery.
How MX Priority Works
Priority is a 16-bit unsigned integer (0-65535). Lower values mean higher preference. A typical configuration looks like this:
- Priority 10:
mail1.example.com(primary) - Priority 20:
mail2.example.com(secondary)
If two MX records share the same priority, the sending server selects between them randomly, which provides basic load balancing. This is a common pattern used by large mail providers to distribute incoming traffic across multiple data centers.
Recognizing Common MX Configurations
Google Workspace
Google Workspace domains use MX records like aspmx.l.google.com at priority 1, with additional servers at priorities 5, 10, 20, and 30. If you see these hostnames, the domain uses Gmail for business email. Validate that all five records are present; partial configurations can cause intermittent delivery failures.
Microsoft 365
Microsoft 365 domains typically have a single MX record pointing to <tenant>.mail.protection.outlook.com at priority 0. The hostname includes the tenant identifier, making it easy to confirm which Microsoft 365 organization owns the domain.
Yahoo Mail
Yahoo's MX records point to servers like mta5.am0.yahoodns.net and related hosts. Consumer Yahoo Mail domains are not configurable, but businesses using Yahoo-hosted email should verify these records resolve correctly.
How to Use This Tool
Enter a domain name into the MX Lookup tool and submit. The tool returns every MX record for the domain, ordered by priority, along with the resolved IP addresses of each mail server and its response status. You will see whether each server accepts SMTP connections on port 25 and whether it presents a valid banner.
Interpreting Your Results
A healthy MX configuration has at least two MX records with different priorities pointing to responsive servers. Watch for these issues:
No MX records found. The domain cannot receive email. If this is unexpected, check whether the DNS zone is properly delegated and that MX records have been created.
MX pointing to an IP address. RFC 5321 explicitly requires MX records to contain hostnames, not IP addresses. Some mail servers will reject delivery in this case.
MX pointing to a CNAME. While some resolvers follow the chain, RFC 2181 discourages this practice. It can cause delivery failures with strict SMTP implementations.
Single MX with no fallback. If the primary server goes down, all inbound mail will queue at the sender and eventually bounce after the retry timeout (typically 5 days per RFC 5321).
MX Records and Email Authentication
MX configuration interacts directly with email authentication protocols. SPF records should authorize the IP addresses of your MX servers if those servers also send outbound mail. Run a SPF Check to verify alignment. For a complete picture of your domain's email health, including SPF, DKIM, DMARC, and MX validation, use the Full Report.
You can also cross-reference MX results with a broader DNS lookup to ensure your domain's overall record set is consistent and correctly configured.
Keep Your MX Records Current
Mail server migrations are one of the most common times for MX misconfiguration. When switching providers, update MX records to point to the new servers, but keep the old records active until you have confirmed the new servers are accepting mail correctly. Lower your TTL before the migration to speed up propagation, and raise it again once the cutover is complete.
FAQ
What is an MX record?
An MX (Mail Exchange) record is a type of DNS record that specifies which mail server is responsible for receiving email on behalf of a domain. Defined in RFC 1035 and RFC 5321, each MX record contains a priority value and a mail server hostname. Without MX records, sending servers have no way to determine where to deliver email for your domain.
How do I look up MX records for a domain?
You can check any domain's MX records using our MX Lookup tool — just enter the domain name and the tool will return all MX records with their priorities, resolved IP addresses, and SMTP connectivity status. Alternatively, you can use command-line tools like dig example.com MX or nslookup -type=mx example.com, though these won't provide the additional validation and diagnostics that our tool includes.
What does MX priority (preference) mean?
MX priority is a numeric value (0-65535) that determines the order in which mail servers are tried during delivery, as specified in RFC 5321. The server with the lowest priority number is contacted first; if it is unreachable, the sending server falls back to the next-lowest value. When two MX records share the same priority, the sending server selects between them randomly, providing basic load balancing.
Can a domain have multiple MX records?
Yes, and it is strongly recommended. Having multiple MX records with different priority values provides failover — if your primary mail server is unavailable, sending servers will automatically attempt delivery to secondary servers. Most major email providers configure between two and five MX records to ensure high availability and distribute load across data centers.
What happens if a domain has no MX records?
If no MX records exist for a domain, the domain cannot receive email through normal MX-based routing. Per RFC 5321, a sending server may fall back to the domain's A or AAAA record as a last resort, but many modern mail servers will not attempt this and will instead return a bounce. Use the MX Lookup tool to verify that your domain's MX records are properly configured and pointing to responsive servers.
How do MX records affect email delivery?
MX records are the foundation of email routing — they direct every inbound message to the correct mail server. Misconfigured MX records can cause bounced emails, delayed delivery, or messages landing at the wrong server entirely. MX configuration also interacts with authentication protocols like SPF; your SPF record should authorize the IP addresses of your MX servers if they send outbound mail. Run a Full Report to check your MX records alongside SPF, DKIM, and DMARC in one pass.
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