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MX Record Lookup
Mail Exchanger (MX) records specify the mail servers responsible for receiving email on behalf of a domain.
RFC:
RFC 1035, RFC 7505
TYPE:
Resource Record
PRIORITY:
Enabled
What is MX Record Lookup?
MX records tell the rest of the internet which mail servers are designated to handle incoming email for your domain. Without a valid MX record, you cannot receive email.
How it Works
Sending servers look up the MX records of the recipient domain. The records contain a priority value and a hostname. The server attempts to deliver to the hostname with the lowest priority value first.
Key Use Cases
Configuring professional email services like Google Workspace or Microsoft 365.
Setting up backup mail servers with higher priority values.
Preventing email spoofing by ensuring valid mail paths.
Advanced Details
MX records must point to a domain name (A or AAAA record), NOT directly to an IP address. Using an IP address in an MX record is technically invalid and can cause delivery failures.
Cybersecurity Pros & Cons
Security Advantages
- Identifying MX providers exposes the email security stack (e.g., Proofpoint, Mimecast) for threat modelling.
- Backup MX servers (higher priority value) ensure continuity during targeted mail server disruptions.
- MX enumeration is a critical OSINT step that reveals phishing infrastructure when spoofed domains are found.
- Port 25 connectivity tests on MX hosts can proactively detect open relay misconfigurations.
Security Limitations
- Publicly visible MX records immediately reveal which email security vendor you use, aiding targeted attacks.
- A single MX record with no backup is a critical SPOF — one DDoS takes down all inbound email.
- Attackers enumerate MX records during reconnaissance to craft credible Business Email Compromise (BEC) lures.
- Misconfigured MX priority values can silently route email to unmonitored backup servers.
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