MX Lookup — Check Any Domain's Mail Server Records Instantly

Learn how MX records work, what mail server priorities mean, how to read common configurations for Google Workspace and Microsoft 365, and how to use a free MX lookup tool to diagnose email routing.

By sadiqbd · June 6, 2026

MX Lookup — Check Any Domain's Mail Server Records Instantly

Email delivery depends on a DNS record most people never think about

When someone sends an email to user@example.com, the sending mail server needs to know which server to deliver it to. It doesn't guess or use the domain's IP address. It looks up the MX records — Mail Exchanger records — in DNS. These records point to the mail servers responsible for receiving email for that domain.

An MX lookup queries DNS and returns the mail servers configured for a domain, along with their priority values.

What MX Records Are

MX (Mail Exchanger) records are DNS records that specify which mail servers accept incoming email for a domain. Every domain that receives email must have at least one MX record.

MX record format:

example.com  MX  10  mail1.example.com
example.com  MX  20  mail2.example.com

Field	Meaning
Name	The domain receiving email
Type	MX
Priority	Lower number = higher priority
Value	Hostname of the mail server

Priority determines the order in which mail servers are tried. A sending server first attempts delivery to the lowest-priority-number server (highest preference). If that server is unavailable, it tries the next highest priority number. This provides built-in redundancy.

Common MX Record Configurations

Google Workspace (Gmail for business)

example.com  MX  1   ASPMX.L.GOOGLE.COM
example.com  MX  5   ALT1.ASPMX.L.GOOGLE.COM
example.com  MX  5   ALT2.ASPMX.L.GOOGLE.COM
example.com  MX  10  ALT3.ASPMX.L.GOOGLE.COM
example.com  MX  10  ALT4.ASPMX.L.GOOGLE.COM

Multiple servers with different priorities ensure delivery even if primary servers are temporarily unavailable.

Microsoft 365 (Exchange Online)

example.com  MX  0   example-com.mail.protection.outlook.com

Single MX record at priority 0 — Microsoft 365's inbound gateway, which handles routing internally.

Zoho Mail

example.com  MX  10  mx.zoho.com
example.com  MX  20  mx2.zoho.com

Self-hosted mail server

example.com  MX  10  mail.example.com

Single MX record pointing to the organisation's own mail server.

How to Use the MX Lookup Tool on sadiqbd.com

Enter the domain name — the domain you want to check email routing for (e.g. example.com)
Run the lookup — the tool queries DNS for MX records
Read the results — all MX records are displayed with their priority values and hostnames

Real-World Examples

Diagnosing email bounces

Someone sends an email to info@example.com and gets a bounce: "Host not found." An MX lookup for example.com reveals:

No MX records found.

Email can't be delivered because there are no mail servers configured to receive it. The domain either never had email configured, or the MX records were accidentally deleted. Solution: add MX records through the domain's DNS provider.

Confirming Google Workspace setup

After setting up Google Workspace for a new domain, you want to verify MX records propagated correctly.

MX lookup for example.com returns:

10  ASPMX.L.GOOGLE.COM
5   ALT1.ASPMX.L.GOOGLE.COM
...

Google's mail servers are present and correctly prioritised. Email will be delivered to Google Workspace.

Checking what mail provider a company uses

MX lookup is a quick way to see who handles email for any domain — useful for competitive intelligence, sales prospecting tools, or email security research.

company.com → mail.protection.outlook.com → they use Microsoft 365 company.com → ASPMX.L.GOOGLE.COM → they use Google Workspace company.com → mx.zoho.com → they use Zoho Mail

Identifying an email security gateway

Some organisations route all inbound email through a security gateway (for spam filtering, malware scanning, or archiving) before it reaches their primary mail server.

MX lookup returns: proofpoint.com, mimecast.com, or similar third-party security platform hostnames as the MX records — indicating all incoming email passes through that vendor's infrastructure before delivery.

Diagnosing MX record priority issues

An organisation has two mail servers but both at the same priority:

example.com  MX  10  mail1.example.com
example.com  MX  10  mail2.example.com

Same priority means senders choose randomly between them (load-balancing intent). If the intent was primary/failover, priorities should differ: mail1 at 10, mail2 at 20. The MX lookup makes this visible.

MX Records and Email Authentication

MX records are for inbound email routing. Email authentication (SPF, DKIM, DMARC) relates to outbound email — proving your emails are legitimate. These are separate but both necessary:

MX records tell the internet where to deliver email to your domain
SPF records (TXT) tell receiving servers which IPs are authorised to send from your domain
DKIM records (TXT) hold the public key for verifying email signatures
DMARC records (TXT) specify the policy and reporting for authentication failures

All of these are DNS records, but they serve different functions. An MX lookup covers the inbound routing side.

No MX Records: Using the Domain Itself

If no MX records exist for a domain, some mail servers will fall back to the domain's A record — attempting delivery directly to the IP address the domain resolves to. This is a historical fallback behaviour that most modern mail servers implement. However, it's unreliable and not a substitute for proper MX records.

Tips for MX Record Management

Always have at least two MX records. A single MX record is a single point of failure. If that server is unreachable, email delivery fails. Two records at different priorities provide failover.

Verify MX records after any DNS migration. Domain transfers and DNS provider changes are common times for MX records to be accidentally overwritten or lost.

Check MX records after switching email providers. If you switch from one mail provider to another, the old MX records must be replaced with the new provider's records. Running the old and new simultaneously causes split delivery.

MX records must point to a hostname, not an IP address. Some DNS providers let you enter an IP in the MX value field. This violates DNS standards and causes delivery failures with compliant mail servers. The MX value must be a hostname (A record), which then resolves to an IP.

Frequently Asked Questions

What does MX priority 0 mean? Priority 0 is the highest possible preference — it will always be tried first. Microsoft 365 commonly uses priority 0 for its single MX record. Lower numbers always mean higher preference.

Can I have MX records pointing to two different mail providers? Technically yes, but it causes split delivery — some email goes to one provider, some to the other, depending on which MX record senders use. This is generally problematic unless you're intentionally doing a phased migration. Use only one provider's MX records at a time for normal operation.

How long does MX record propagation take? Same as other DNS records — typically a few minutes to a few hours, up to 48 hours in rare cases depending on the TTL of the old records and resolver caching.

Does changing MX records affect outbound email? No — MX records only affect inbound routing. Outbound email delivery is controlled by your mail server configuration and SPF records, not MX records.

Is the MX lookup tool free? Yes — completely free, no sign-up required.

MX records are foundational for email — without them, nobody can send email to your domain. The lookup tool gives you the current state of any domain's mail routing in seconds, which is invaluable for setup verification, troubleshooting, and competitive research.

Try the MX Lookup tool free at sadiqbd.com — check any domain's mail servers and priorities instantly.