The 9 fields and concepts you'll meet in the response — defined in plain English, each with a real example value.
A DNS record specifying mail servers responsible for receiving email for a domain.
MX (Mail Exchange) records contain a priority value and hostname. Sending servers query MX records to find where to deliver email. Multiple MX records provide redundancy. Priority determines the order servers are tried—lower numbers first.
Exampleexample.com MX 10 mail.example.com
A number indicating the preference order for MX records—lower values mean higher priority.
Also called "preference," priority determines which mail server to try first. Priority 10 is tried before priority 20. If the primary fails, senders try backups in order. Equal priorities result in random load balancing between servers.
ExamplePriority 10 (primary), Priority 20 (secondary), Priority 30 (backup)
A server that receives, routes, and stores email messages.
Mail servers run SMTP for sending/receiving, IMAP/POP3 for client access. MX records point to mail server hostnames. Major providers (Google, Microsoft) run highly available mail server infrastructure. Self-hosted mail servers require significant security expertise.
Exampleaspmx.l.google.com, mail.protection.outlook.com
Simple Mail Transfer Protocol—the standard for sending email between servers.
SMTP handles server-to-server email transmission, typically on port 25. SMTP uses MX records to find destination servers. Modern SMTP uses STARTTLS for encryption. SMTP defines how email is addressed, transmitted, and acknowledged.
ExampleSMTP connects to MX server on port 25
A service that hosts email for domains, identifiable by MX record patterns.
Email providers like Google Workspace, Microsoft 365, and Zoho have distinctive MX record patterns. MX lookup reveals which provider a domain uses. This is useful for sales intelligence, competitive analysis, and email deliverability research.
ExampleGoogle Workspace: aspmx.l.google.com, Microsoft 365: mail.protection.outlook.com
Sender Policy Framework—a DNS record listing IPs authorized to send email for a domain.
SPF prevents email spoofing by letting domain owners specify authorized senders. Receivers check if the sending IP is listed in SPF. Failures can trigger rejection or spam filtering. SPF is published as a TXT record.
Examplev=spf1 include:_spf.google.com ~all
DomainKeys Identified Mail—cryptographic email signing for message authenticity.
DKIM adds digital signatures to email headers. The public key is published in DNS. Receivers verify signatures to confirm messages weren't altered. DKIM proves both sender authenticity and message integrity.
ExampleDKIM-Signature: v=1; a=rsa-sha256; d=example.com; s=selector
Domain-based Message Authentication, Reporting & Conformance—policy for email authentication.
DMARC tells receivers what to do when SPF/DKIM fail: reject, quarantine, or none. It also configures reporting—aggregate and forensic reports. DMARC ties SPF and DKIM into unified policy. Published as a TXT record at _dmarc.domain.com.
Examplev=DMARC1; p=reject; rua=mailto:[email protected]
Automatic switching to backup servers when primary servers are unavailable.
Multiple MX records with different priorities provide email failover. If the primary server (priority 10) is down, senders try the secondary (priority 20). This ensures email delivery even during outages. Good configurations have at least two MX records.
ExamplePrimary fails → sender tries secondary → email delivered
