Example result
The input https://Vercel.com/pricing, cut down to the domain vercel.com, read through Cloudflare's DNS over HTTPS on 2026-10-19.
- Verdict
- 5 mail servers found for vercel.com. Mail is handled by Google Workspace.
- Priority 1
- aspmx.l.google.com
- Priority 5 (shared load)
- alt1.aspmx.l.google.com, alt2.aspmx.l.google.com
- Priority 10 (shared load)
- aspmx2.googlemail.com, aspmx3.googlemail.com
- Provider
- Google Workspace, on all 5 hosts
- Unidentified hosts
- None
Captured 2026-10-19.
How it works
- Type a domain. A pasted link or email address is cut down to its domain name.
- Your browser asks a public DNS resolver for the MX records. If there are none, it also asks for the A and AAAA records of the domain, which senders use as a fallback.
- The page lists each host with its priority, lowest first, names the provider from the host name, and says whether the domain has MX records, a null MX or neither.
How senders use MX records
Every MX record has a priority number and a host. A sending server tries the host with the lowest number first and moves up if that host does not answer. Hosts that share a number are tried in no fixed order, so they share the load between them. RFC 5321 section 5.1 sets these rules.
The priority number is only a ranking. 10 and 20 mean the same thing as 1 and 2: the first is tried before the second. Large numbers are not worse, and a gap between numbers means nothing.
Three states that look alike
MX records present: the domain accepts mail at the hosts listed. Null MX: a single record with priority 0 and the host "." tells senders the domain accepts no mail at all, as RFC 7505 defines. Priority 0 with a real host name is an ordinary record, and many working domains use it, so the page does not call it a null MX.
No MX record: this is the ambiguous one. RFC 5321 says senders then treat the domain itself as the mail host, using its A or AAAA address, as if it had an MX record of priority 0 pointing at itself. So the page also reports whether an address record exists. With neither an MX nor an address record, a domain cannot receive mail. A name that does not exist in DNS is reported on its own.
Reading the provider
The provider is read from the ending of each host name, using a table we keep. If a host matches no row, the page says unidentified rather than guessing. When hosts point at more than one provider, every match is listed. A mail filter placed in front of a mailbox service, such as an email security gateway, shows as the filter, because that is the name in the MX records.
MX records cover receiving only. To see who is allowed to send for a domain, use the SPF record checker.
Provider host name endings we match, with an example host for each
| Provider | Host name ends with | What it is | Example host |
|---|---|---|---|
| Google Workspace | google.com, googlemail.com | Mailbox host | aspmx.l.google.com |
| Microsoft 365 and Outlook.com | protection.outlook.com | Mailbox host | github-com.mail.protection.outlook.com |
| Proofpoint | pphosted.com, ppe-hosted.com, proofpoint.com | Email security gateway | mx0a-00148501.pphosted.com |
| Mimecast | mimecast.com, mimecast.co.za, mimecast-offshore.com | Email security gateway | service-alpha-inbound-a.mimecast.com |
| Barracuda | barracudanetworks.com | Email security gateway | d160221a.ess.barracudanetworks.com |
| Cisco Secure Email | iphmx.com | Email security gateway | mx1.hc2186-24.iphmx.com |
| Cloudflare Email Routing | mx.cloudflare.net | Forwarding or inbound service | route1.mx.cloudflare.net |
| Cloudflare Email Security | cf-emailsecurity.net | Email security gateway | mxa.global.inbound.cf-emailsecurity.net |
| Fastmail | messagingengine.com | Mailbox host | in1-smtp.messagingengine.com |
| Proton Mail | protonmail.ch | Mailbox host | mail.protonmail.ch |
| Zoho Mail | zoho.com, zoho.eu, zoho.in, zoho.com.au, zoho.jp, zoho.com.cn, zohomail.com | Mailbox host | mx.zoho.com |
| Amazon SES (inbound) | inbound-smtp.*.amazonaws.com | Forwarding or inbound service | inbound-smtp.us-east-1.amazonaws.com |
| Apple iCloud Mail | icloud.com | Mailbox host | mx01.mail.icloud.com |
| Yahoo Mail | yahoodns.net | Mailbox host | mta5.am0.yahoodns.net |
| Namecheap Private Email | privateemail.com | Mailbox host | mx1.privateemail.com |
| Mailgun (inbound) | mailgun.org | Forwarding or inbound service | mxa.mailgun.org |
| Forward Email | forwardemail.net | Forwarding or inbound service | mx1.forwardemail.net |
Sources
- RFC 5321: Simple Mail Transfer Protocol, section 5.1 locating the target host read 2026-10-19
- RFC 7505: A "Null MX" No Service Resource Record for Domains That Accept No Mail read 2026-10-19
- Cloudflare 1.1.1.1 documentation: DNS over HTTPS, using JSON read 2026-10-19
- Google Public DNS: DNS over HTTPS JSON API read 2026-10-19
- Google Workspace Admin Help: set up MX records for Google Workspace email read 2026-10-19
- Cloudflare Email Routing documentation: DNS records read 2026-10-19
- Fastmail Help: manual DNS configuration read 2026-10-19
- Zoho Mail Help: configure email delivery read 2026-10-19
- Amazon SES Developer Guide: MX record for receiving email read 2026-10-19
This tool is run by LookValid. It is not connected to any agency, company or service named on this page.
Frequently asked questions
What does the priority number mean?
It ranks the hosts. A sender tries the lowest number first and moves to the next only if that host cannot be reached. Hosts with the same number share the load. The numbers themselves carry no other meaning.
What is a null MX?
A single MX record with priority 0 and the host "." (RFC 7505). It tells senders that the domain accepts no mail, so they can stop at once instead of retrying for days. Priority 0 with a real host name is an ordinary MX record and is not a null MX.
Can mail still reach a domain that publishes no MX record?
Yes, if it has an A or AAAA record and a mail server is running at that address. RFC 5321 tells senders to fall back to the domain itself when no MX exists. Publishing an explicit MX record is clearer and is what most mail providers ask for.
Why does the provider say unidentified?
The host names do not end with any ending in our table. That is common for self-hosted mail and small hosting companies. It does not mean anything is wrong with the records.
Does the provider show where my mailboxes live?
Not always. The MX records name the first server that receives mail. A filter or forwarding service in front of the mailbox service shows up instead of the mailbox host, and the filter passes the mail on.
Why does the check say it could not finish?
The DNS resolver did not answer in time or reported a server failure. That says nothing about whether MX records exist, so it is not reported as missing. Run the lookup again in a moment.