Email Domain Checker
Verify whether an email domain can receive mail and understand what its DNS records reveal.
What Is an Email Domain Check?
An email domain check verifies whether a domain is configured to receive email. This involves looking up the domain's MX (Mail Exchange) records in DNS. If no MX records exist, the domain cannot receive email, and any address at that domain is effectively undeliverable.
What DNS Records Reveal About an Email Domain
MX Records
MX records specify the mail servers responsible for accepting email on behalf of a domain. They include a priority value and a hostname. For example, a domain using Google Workspace might have:
10 aspmx.l.google.com20 alt1.aspmx.l.google.com30 alt2.aspmx.l.google.com
The lowest priority number indicates the primary mail server.
SPF (Sender Policy Framework)
SPF is a TXT record that lists the IP addresses and hostnames authorized to send email from the domain. It helps receiving servers detect spoofing. An SPF record for a Microsoft 365 domain typically includes include:spf.protection.outlook.com.
DKIM (DomainKeys Identified Mail)
DKIM adds a cryptographic signature to outgoing email, allowing recipients to verify the message was not tampered with in transit. DKIM is configured using CNAME or TXT records that reference the provider's signing keys.
DMARC
DMARC builds on SPF and DKIM to provide instructions for what recipients should do if email fails authentication. It is published as a TXT record on the _dmarc subdomain.
How the Email Provider Filter Checks Domains
When you submit email addresses to the tool, it performs the following for each unique domain:
- Validates email syntax (correct format with a valid domain part).
- Queries DNS for MX records to confirm the domain can receive email.
- Queries DNS for TXT/SPF records to identify the authorized sending infrastructure.
- Matches the combined DNS results against known provider signatures.
- Groups valid emails by provider and flags invalid ones.
Domains are cached within a single request, so if you submit 100 emails across 10 domains, only 10 DNS lookups are performed.
Common Domain Check Scenarios
- No MX records — the domain cannot receive email; all addresses at this domain are invalid.
- MX records present but no provider match — the domain uses a custom or lesser-known mail server that is not in the tool's provider signature database.
- Filtering service in MX, provider in SPF — the domain uses a service like Mimecast or Proofpoint for inbound filtering, but the actual mail platform is identifiable through SPF.
- Multiple providers — some domains have mixed DNS records due to migrations or hybrid configurations. The tool reports the strongest match.
Related Resources
- MX Record Checker — detailed guide to MX records
- Email Provider Lookup — how provider identification works
- What DNS Records Tell You About an Email Domain
- How Email Domain Lookup Works