--- title: Free MX Lookup description: List a domain's mail servers — every MX record with its priority and TTL, exactly as sending servers see it. Verify a Google Workspace or Microsoft 365 cut-over, find the leftover MX that still points at the old provider, and explain why mail is bouncing. canonical: https://watchfor.io/mx-lookup --- [Back to all free tools](/free-tools) # MX Lookup List a domain's mail servers — every MX record with its priority and TTL, exactly as sending servers see it. Verify a Google Workspace or Microsoft 365 cut-over, find the leftover MX that still points at the old provider, and explain why mail is bouncing. Result No result yet Enter the inputs above and press Run. Results appear here in a moment. Monitor this 24/7 — get alerts on the first failure. [Start free](/auth/sign-up) Only run these tools against systems you own or are authorized to test. Using them to scan or probe systems without permission violates our [Terms](/legal/terms). ## What is MX Lookup ? MX records tell the world which servers accept email for a domain, and in what order. When someone sends mail to you@example.com , their server looks up the MX records of example.com , sorts them by priority (lowest number first), and tries to deliver to each in turn. No MX records, no inbound mail — the sender falls back to the domain's A record, which is almost never a mail server, and the message bounces days later with an error nobody reads. This tool lists a domain's MX records exactly as sending servers see them: each mail host, its priority, the TTL, and the resolver that answered. It's the first check after moving to Google Workspace or Microsoft 365, the fastest way to find the leftover MX that still points at the previous provider, and the honest answer to "is it our DNS or their server" when mail isn't arriving. ## How it works The lookup follows RFC 5321's delivery rules: - 1 Query `QTYPE=MX` for the domain — Against the resolver you chose — or against the domain's own authoritative nameserver, which is the only way to see a change before caches expire. - 2 Read priority and target — Each record is a preference number and a hostname. Lower preference is tried first; equal preferences are load-balanced. The hostname must resolve to an A or AAAA record — not a CNAME. - 3 Show what a sender would do — Records sorted as an MTA would sort them, with TTLs so you know how long the old answer will persist after a change. To go further, test the mail host itself: the SMTP server test connects to it on port 25 and reports the banner, STARTTLS and whether it relays for strangers. ## When you'd use it ### After switching email providers Google Workspace wants smtp.google.com (or the older five aspmx hosts); Microsoft 365 wants example-com.mail.protection.outlook.com . Look up the MX set: the provider's records must be there and the old provider's must be gone, or mail splits between two inboxes. ### "Your emails aren't arriving" The customer says they sent it; you never got it. Their server delivered to whatever your MX said at the time. If the MX points at a decommissioned host or a typo, the bounce went to them and the blame came to you. ### Setting up a domain that only sends Transactional-only domains still need an MX (or a null MX, 0 . ) so that senders and spam filters can see the domain is deliberately not receiving mail, rather than misconfigured. ### Checking a partner or customer domain Before opening a ticket with them, see what their MX says. A domain with no MX, or an MX pointing at a name that doesn't resolve, explains a lot of "we never got your invoice". ## Reading the result ### Priority (preference) Lowest number wins; senders try higher numbers only if the lower ones fail to connect. 10 mx1 , 20 mx2 means mx2 is the backup. Two records with the same number share the load. ### Mail host Must be a hostname with an A/AAAA record. An IP address here is invalid; a CNAME is against the spec and refused by strict senders. ### Null MX A single record 0 . (priority 0, target a bare dot) says the domain accepts no mail at all (RFC 7505). Senders bounce immediately instead of retrying for days. ### No MX records at all Senders fall back to the domain's A record and try SMTP there. If a web server answers on port 25 — it doesn't — mail would go there. In practice, mail bounces after the retry window. ## Check it yourself dig MX example.com @1.1.1.1 +noall +answer dig MX example.com @ns1.example.com asks the authoritative server directly and shows a change before any cache has expired. ## Common pitfalls ### Old provider's MX left in place The most common migration bug: new records added, old ones not removed. Some mail lands at the old provider (if it still accepts it) and quietly disappears. Remove them — don't just raise their priority number. ### Pointing MX at a CNAME RFC 2181 forbids it. Some senders follow the alias, some refuse the message. Use the real hostname. ### Forgetting SPF, DKIM and DMARC MX is inbound. The outbound side — proving your mail is really from you — lives in TXT records. A new provider's MX without an updated SPF include: gets your outbound mail marked as spam. ## Run MX Lookup on every change, not just once. Get alerts the moment something breaks — across HTTP, DNS, SSL, RDAP, ping, blacklist and more. Free forever for 10 monitors. No card. [Start free](/auth/sign-up) ## Frequently asked questions What are the MX records for Google Workspace? Since 2023 a single record: 1 smtp.google.com . Older setups use five: 1 aspmx.l.google.com , 5 alt1.aspmx.l.google.com , 5 alt2.aspmx.l.google.com , 10 alt3.aspmx.l.google.com , 10 alt4.aspmx.l.google.com . Both still work; don't mix them with another provider's. What is the MX record for Microsoft 365? One record shaped 0 .mail.protection.outlook.com , for example 0 example-com.mail.protection.outlook.com . The exact value is shown in the Microsoft 365 admin center under Domains. What does the MX priority number mean? Order of delivery attempts: lowest first. It's relative — 10 / 20 behaves exactly like 1 / 2 . Equal numbers are tried in random order for load sharing. Can I have one MX record? Yes, and most cloud providers use exactly one, because the hostname itself resolves to many redundant addresses. Multiple MX records mainly matter when you run your own backup server. How long after changing MX records does mail switch over? Sending servers use the records they resolve at send time, so after the old TTL expires (commonly an hour) all new mail goes to the new host. Mail already queued at the old host stays there. Do subdomains need their own MX records? Yes — mail@sub.example.com is delivered according to sub.example.com 's MX records, not the parent's. A subdomain with no MX and no A record bounces. ## Related dns tools - [DNS LookupResolve A, AAAA, MX, TXT, NS, SOA, CNAME, PTR, CAA, SRV records for any domain.](/dns-checker) - [DNS PropagationCheck how a DNS record looks from every prober region simultaneously — spot stale anycast nodes and propagation gaps on a world map.](/dns-propagation-checker) - [Whois LookupModern RDAP-based domain registration lookup: registrar, expiry, nameservers, status flags.](/whois-lookup) - [A Record LookupFind the IPv4 address a domain resolves to — every A record with its TTL, from the resolver of your choice. Spot a stale IP after a migration, a missing record behind a 'site can't be reached', or a round-robin set that is one address short.](/a-record-lookup) --- Canonical page: https://watchfor.io/mx-lookup · Site guide: https://watchfor.io/llms.txt