The MX records tell other mail servers where to deliver email for a domain. This lookup lists them by preference, resolves each host to an IP address and checks its reverse DNS, which receiving and sending servers both rely on.
Table of Contents
What to look for
Lower preference numbers are tried first. Every MX host must resolve to an A or AAAA record — an MX pointing at a CNAME or an IP address breaks delivery at strict senders. A mail server’s IP should have a PTR record that resolves back to the same hostname (forward-confirmed reverse DNS).
If the domain uses Microsoft 365 or Google Workspace you will see their hosts here; if you expected your own server, the MX was changed at some point and mail is going elsewhere.
MX lookup at a glance
How to use this tool
- Enter the domain part of the email address: for
info@example.comenterexample.com. A pasted URL is reduced to the host name. - Press Look up MX. The tool reads the MX records through Cloudflare’s resolver (1.1.1.1), sorts them by preference, resolves each mail host to an IP address and checks the reverse DNS of that IP.
- Read the summary first: the number of MX records and how many hosts have a resolving IP with a matching PTR. Any amber row deserves a look.
- Check the listed IP addresses on the IP blacklist check, and test the mail server itself (banner, STARTTLS, certificate) with the SMTP test.
The result for the same domain is cached for five minutes. After changing MX records, use the DNS propagation checker with type MX to watch resolvers pick up the change.
How to read the results
| Field | What it means |
|---|---|
| MX records | The number of MX records found. “None” (red) means senders fall back to the domain’s A record, which most treat as a misconfiguration. |
| Hosts with resolving IP and matching rDNS | How many MX hosts passed all three checks: the host name resolves, its IP has a PTR record, and that PTR name resolves back to the same IP. |
| Pref | The preference value. Senders try the lowest number first and use higher numbers only when it fails. Equal values share the load. |
| Host | The mail server name from the MX record. |
| Green / amber dot | Green when the host resolves and has forward-confirmed reverse DNS. Amber when any of the three checks fails. |
| IP | The first IPv4 address of the host, or the first IPv6 address when there is no A record. “does not resolve” means the host name has neither. |
| Reverse DNS with a check mark | The PTR name of the IP, confirmed: it resolves back to the same IP. |
| “(not forward-confirmed)” | The IP has a PTR name, but that name does not resolve back to the IP. |
| “no PTR” | The IP has no reverse DNS record at all. |
Reverse DNS on an inbound MX host matters less than on a sending server, because senders do not normally refuse to deliver to a host without a PTR. It still matters in practice: the same server usually sends mail too, and Gmail requires sending IPs to have a PTR that resolves back to the same IP.
Common problems and how to fix them
An MX host shows “does not resolve”
The MX points at a name without an A or AAAA record. Common causes: mail.example.com was deleted during a website move, the mail provider changed host names, or a BIND-style zone entry was written without the trailing dot, so mail.example.com became mail.example.com.example.com. Create the missing A record or correct the MX value.
; wrong (no trailing dot, the zone name is appended)
example.com. 3600 IN MX 10 mail.example.com
; right
example.com. 3600 IN MX 10 mail.example.com.
mail.example.com. 3600 IN A 203.0.113.10A row with preference 0, an empty host and “does not resolve”
This is a null MX record (0 ., RFC 7505). It declares that the domain receives no email, and senders bounce immediately instead of retrying. That is correct for parked domains and domains that only host a website. If the domain should receive mail, replace it with real MX records; a null MX must never be combined with other MX records.
Reverse DNS shows “no PTR” or “(not forward-confirmed)”
Only the owner of the IP block can set the PTR record: your hosting provider, VPS provider or ISP, usually through a control panel or support ticket. Ask for the PTR to be set to the server’s host name (for example server1.example.com), then make sure that name has an A record with the same IP. On cPanel servers the host name is set in WHM under Networking Setup, Change Hostname, and Exim announces it in the SMTP banner. Check the result with the reverse DNS lookup.
MX points to Microsoft 365 or Google, but some mail still lands on the old server
The hosting server still thinks it is responsible for the domain’s mail, so messages sent from that server (contact forms, other accounts on it) are delivered locally and never leave. In cPanel open Email Routing and select Remote Mail Exchanger. In DirectAdmin open the MX records page and untick Use this server to handle my e-mails. See external mail with DirectAdmin for the full checklist.
The MX host resolves to a Cloudflare IP
The A record of the mail host is proxied (orange cloud). Cloudflare proxies web traffic only, so SMTP to that IP fails. Set the mail host record to DNS only (grey cloud). A common slip is reusing the proxied A record of the website (for example the apex) as the mail host.
MX records from two providers are mixed
After a migration, an old mail.example.com record sometimes remains next to the new provider’s MX at a different or equal preference. Senders then deliver part of the mail to the old server. Remove every MX that does not belong to the current provider, and keep the old mailbox server running for a few days to collect late deliveries.
Typical MX records for common mail providers
| Provider | MX record |
|---|---|
| Google Workspace (current) | One record: smtp.google.com, priority 1. Domains set up before 2023 may still use the older aspmx.l.google.com set, which keeps working. |
| Microsoft 365 | One record pointing at example-com.mail.protection.outlook.com (your domain with dashes). Copy the exact value from the Microsoft 365 admin center under Domains. |
| cPanel or DirectAdmin server | Usually mail.example.com or the domain itself, with an A record pointing at the server IP. |
| Domain that sends but never receives | Null MX 0 ., together with SPF and DMARC. |
From the command line you can check the same thing with dig MX example.com +short on Linux or macOS, or Resolve-DnsName example.com -Type MX in Windows PowerShell.
Official documentation: DirectAdmin documentation, cPanel & WHM documentation, RFC 5321 (SMTP).
Related guides: Warm up a new mail server IP or sending domain without landing in spam · Whitelisting MailBaby in cPanel greylisting, CSF and SpamAssassin · Email forwarders with MailBaby: SRS, strict forwarding errors and backoffs.
Frequently asked questions
What happens if a domain has no MX record?
Senders fall back to the domain’s A record, which rarely runs a mail server, so mail usually fails or bounces. Publish an MX even if you only receive mail on one server.
Can an MX record point to an IP address?
No. RFC 5321 requires a hostname. Create an A record such as mail.example.com and point the MX at that.
Do backup MX servers still make sense?
Rarely. Modern senders retry for several days, and backup MX hosts with weaker filtering are a common spam path. Only use one if it has the same filtering as the primary.
What is a null MX record?
An MX record with preference 0 and “.” as host, defined in RFC 7505. It tells senders the domain accepts no mail, so they bounce at once instead of retrying for days.
Does the MX preference number have to be 10?
No. Only the order matters: lower numbers are tried first. Values such as 0, 1, 5 or 10 all work, and equal values spread the load.
How long does it take for an MX change to work?
As long as the old MX record’s TTL, because senders cache it. Google says to allow up to 72 hours for a new Workspace MX to be recognised; with a short TTL it is usually much faster.
Why is mail from my website not reaching Microsoft 365 after changing MX?
The hosting server is probably still set to handle mail locally. Switch cPanel Email Routing to Remote Mail Exchanger, or untick “Use this server to handle my e-mails” in DirectAdmin.
Which IP does the tool show when a host has several addresses?
It shows the first IPv4 address, or the first IPv6 address when the host has no IPv4 address, and checks reverse DNS for that IP.
Can I use the same mail server for many domains?
Yes. Any number of domains can point their MX at the same host name, as long as the server accepts mail for each of them.