Free tool
MX lookup: MX records, priorities and mail provider
Enter a domain to look up its MX records.
Reads the MX records, then the A and AAAA records of every mail server. Lookups go from your browser to Cloudflare's public DNS resolver.
- MX hosts by priority
- The mail provider behind each host
- IPv4 and IPv6 addresses of every host
- SPF checked against the same provider
About this tool
About the MX lookup
MX records name the mail servers that receive email for the domain; senders try the lowest priority number first. Google Workspace's current record is smtp.google.com at priority 1, and Microsoft 365 uses <your-domain>.mail.protection.outlook.com.
The lookup shows each host with its priority, the provider it belongs to and its IPv4 and IPv6 addresses, flags hosts that do not resolve, null MX and mixed providers, and checks that SPF allows the same provider. The lookups run in your browser.
How it works
How to read the MX lookup
Senders look up the MX records, sort them by priority and deliver to the lowest number that answers. Hosts with the same number share the load. Every host must resolve to an address, or mail queued for it waits and then bounces.
- No MX records (error): replies and bounces have nowhere to go; add the records your mailbox provider gives you
- Null MX, a single record "0 ." (note): the domain declares it receives no mail (RFC 7505); fine for a domain that only redirects, wrong for a sending domain
- A host that does not resolve, or an IP address used as MX (errors): senders skip it; fix the name or replace it with the provider's host
- A host that is a CNAME (warning): RFC 2181 says MX must name the real host; most senders cope, some do not
- Two providers in the MX records (warning): mail goes to whichever answers first, so some replies land where nobody reads them
- SPF that misses the provider (note): mail hosted at Google or Microsoft is usually sent through it too, so its include belongs in the SPF record
Background
MX records of common providers
- Google Workspace: smtp.google.com at priority 1; domains set up before 2023 may use aspmx.l.google.com with four alternates, which Google says keep working
- Microsoft 365: <your-domain-with-dashes>.mail.protection.outlook.com at priority 0, shown in the Microsoft 365 admin center under Settings, Domains
- Zoho Mail, Proton Mail, Fastmail, iCloud and others are recognized by host name in the result
- Mail security gateways (Mimecast, Proofpoint, Barracuda, Cisco) sit in front of the mailbox provider; their hosts in MX are normal
Background
MX on cold email domains
A cold email domain needs MX records even when you never read its inbox through a mail client: replies, out-of-office answers and bounces arrive there, and a domain that cannot receive mail looks like it was set up only to send. Domains for cold email covers the full setup.
MX is one of four records a sending domain needs. Check SPF, DKIM and DMARC next, or all four at once in the SPF, DKIM and DMARC checker.
Free guide19 min read
Send 100,000 cold emails a month
Domains and mailboxes you need, DNS, warm-up, lists, copy and follow-ups, with a launch checklist, sent to your inbox.
Questions
How do I look up MX records?
Enter the domain above. By hand: dig MX example.com, or nslookup -type=mx example.com on Windows.
What does the MX priority number mean?
Senders try the lowest number first and move to the next when it does not answer. Hosts with the same number share the mail between them. The numbers only matter relative to each other.
What are Google Workspace's MX records?
smtp.google.com at priority 1. Domains set up before 2023 may have the older set: aspmx.l.google.com at 1, alt1 and alt2 at 5, alt3 and alt4 at 10. Google says both work.
What are Microsoft 365's MX records?
One record: your domain with dots replaced by dashes, followed by .mail.protection.outlook.com, at priority 0. The exact value is in the Microsoft 365 admin center under Settings, Domains.
Do MX records affect sending?
Not directly: MX is for incoming mail. A sending domain still needs them so replies and bounces arrive, and some receivers distrust mail from a domain that cannot receive any.
How long do MX changes take?
As long as the old record's TTL, often 1 to 4 hours, sometimes up to 48. Senders that cached the old record deliver there until it expires.
Does this tool store the domains I check?
No. The lookups go from your browser to Cloudflare's public DNS resolver. We receive nothing unless you ask us to email you the fixes.
In your AI assistant
Run the same checks in Claude or ChatGPT
Free SKILL.md files with the rules behind this tool. Install them in Claude or Claude Code, or paste them into ChatGPT, Gemini, Grok or Cursor.
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