The MX Lookup tool allows you to instantly see the mail servers responsible for receiving emails for any given domain name, along with their priority values. By querying the live Domain Name System, this utility reveals the underlying email infrastructure and helps you diagnose delivery issues.
What is it
An MX (Mail Exchange) record is a type of resource record in the Domain Name System that specifies where email sent to your domain should be routed. When someone sends a message to an address like user@example.com, the sender's mail server queries the DNS for example.com's MX records to find out which server actually accepts incoming mail.
MX records consist of two main components: a priority number and a mail server hostname. The priority number determines the order in which sending servers attempt delivery. Lower numbers represent higher priority. For example, a server with a priority of 10 is contacted before a server with a priority of 20.
If the primary mail server is unreachable or offline, the sending server automatically falls back to the server with the next lowest priority number. This built-in redundancy ensures that your organization continues to receive messages even during temporary server maintenance or localized outages.
Why it matters
Misconfigured or missing MX records are the single most common reason legitimate emails fail to reach a domain. Without correct records, your domain cannot receive inbound messages, resulting in bounced emails and lost business communications.
Verifying your MX records is also essential during domain migrations and email provider transitions. When moving from a legacy on-premises Microsoft Exchange server to a cloud provider like Google Workspace or Microsoft 365, updating your MX records directs incoming traffic to your new inbox. Checking these records confirms that the transition completed successfully and that no messages are still routing to your old host.
Furthermore, security audits rely on inspecting MX records. Knowing which mail servers handle your traffic helps you verify that your corporate mail flows through authorized enterprise gateways rather than unsecured endpoints.
How to use this tool
- Navigate to the XiaTools MX Lookup page in your web browser.
- Locate the search input field in the middle of the screen.
- Type your target domain name into the box, such as example.com.
- Click the Check button to initiate the live DNS query.
- Review the resulting list of mail servers and their corresponding priorities.
How to read the results
When you run a lookup for example.com, the tool returns a table of active mail exchange records retrieved directly from authoritative nameservers. A typical output looks like this:
- Priority: 10 | Mail Server: mail.example.com | Provider: Custom/On-Premises
- Priority: 20 | Mail Server: backup.example.com | Provider: Custom/On-Premises
Alternatively, if the domain uses a major cloud provider, you might see entries pointing to their specific infrastructure:
- Priority: 1 | Mail Server: ASPMX.L.GOOGLE.COM | Provider: Google Workspace
- Priority: 5 | Mail Server: ALT1.ASPMX.L.GOOGLE.COM | Provider: Google Workspace
The priority number dictates the delivery sequence. The mail server hostname must resolve to a valid IP address via A or AAAA records. The provider label helps you quickly identify whether the domain relies on Google, Microsoft, Zoho, or a custom hosting environment.
Common problems and how to fix them
Missing MX Records
A domain with no MX records cannot receive mail, causing senders to receive a permanent delivery failure notification. To fix this, log into your DNS registrar or hosting provider's control panel and add the appropriate MX record supplied by your email host.
example.com. IN MX 10 mail.example.com.
Incorrect Priority Values
If all your MX records share the exact same priority, mail servers will distribute traffic randomly rather than following a primary and secondary failover sequence. Assign distinct numbers, such as 10 for your primary gateway and 20 for your backup gateway.
MX Points to an IP Address
An MX record must always point to a valid domain name hostname, never directly to an IPv4 or IPv6 address. If your DNS provider accepts an IP address in the MX field, email delivery will fail globally.
; Incorrect
example.com. IN MX 10 192.0.2.1
; Correct
example.com. IN MX 10 mail.example.com.
Conflicting CNAME Records
RFC standards prohibit a domain from having a CNAME record and any other record type, including MX records, at the apex or root level. If your root domain has a CNAME record, your MX records will be ignored by receiving servers.
Best practices
Always maintain at least two distinct mail servers with different priority values to ensure high availability and redundancy. If your primary email provider experiences an outage, your secondary backup server can queue incoming messages until service is restored.
Keep your TTL (Time to Live) settings balanced before making changes. Lowering your TTL to 300 seconds a day before a planned migration allows DNS changes to propagate rapidly across the global internet. Once the migration is stable, raise the TTL back to standard intervals like 3600 seconds to reduce lookup queries.
Finally, regularly audit your DNS records using this tool to detect unauthorized changes or leftover configurations from previous email providers that could compromise your mail delivery.