Does a missing MX record mean an email address is bad?

Key findings

• Direct Reception Impact: A domain without an MX record cannot receive email directly from other mail servers that perform standard MX lookups.
• RFC Fallback: According to RFC 5321 (Section 5.1), if no MX records are returned, the mail server should fall back to using the domain's A record as an implicit MX record. This means an email address can still theoretically receive mail if the A record points to a host configured to accept it.
• Deliverability Indication: While a missing MX record doesn't strictly mean an email address is bad for sending, it is often an indicator that the domain is not actively used for email, or it's misconfigured, potentially leading to deliverability issues for recipient addresses. However, it's less likely to impact the sender's deliverability significantly if the email is a hard bounce (and thus not causing spam complaints).
• Email Validation Tools: Many email validation services will flag domains without MX records as invalid, as they assume no mail service is configured, despite the RFC fallback. This is often a practical choice for bulk senders to maintain list hygiene.

Key considerations

• Recipient Intent: A domain without MX records is very likely not set up to receive emails. Even if an A record exists, the server at that IP address might not be configured as a mail server. This typically results in a bounce.
• List Hygiene: For email marketers, including addresses on domains with missing MX records in your sending list is generally not advisable. These will likely hard bounce, affecting your overall deliverability metrics and potentially harming your sender reputation.
• Technical Checks: You can verify the absence of an MX record by performing a DNS lookup specifically for MX records. Tools like dig or nslookup (with @ipaddr for dig or by appending the nameserver IP for nslookup) can be used to confirm this.
• A Record Importance: While an MX record directs mail to a specific mail server, an A record provides the IP address for the domain itself. If no MX record is present, the system may fall back to the A record. Understanding this is key to assessing the complete DNS setup for email.

Key opinions

• Pragmatic Invalidity: Most marketers consider an address on a domain with no MX record to be a 'bad' address for all practical purposes, even if a technical fallback exists.
• List Cleanliness Priority: Prioritizing list hygiene means removing or never adding email addresses from domains that lack proper MX records, as they are very likely to result in hard bounces.
• Beyond MX Checks: Marketers often use comprehensive email validation services that go beyond just checking for MX records, also looking at SPF, DKIM, and other factors to determine email validity.
• Impact on Reputation: While a single hard bounce might not significantly harm reputation, sending to many such addresses over time can signal poor list management to mailbox providers and potentially lead to blocklisting.

Key considerations

• Pre-send Validation: Always validate email lists before sending, especially for new contacts or old lists, to filter out addresses on domains with missing MX records. This proactively prevents bounces.
• Monitoring Bounces: Pay close attention to your bounce rates. High bounce rates from unknown user or host errors can signal underlying issues like non-existent domains or missing MX records.
• Data Source Investigation: If you find a significant number of addresses on domains without MX records, investigate the source of your email addresses. This may indicate issues with your lead generation or data collection processes.
• Understanding DNS Basics: A foundational understanding of DNS records, including MX and A records, empowers marketers to better troubleshoot deliverability issues and maintain healthy lists.

Key opinions

• Not Definitive: Experts highlight that a missing MX record isn't a definitive sign that a domain has no email addresses, due to the RFC fallback to A records, but practically it often is.
• RFC Compliance vs. Reality: While RFCs allow for a fallback to A records, in practice, many mail servers expect explicit MX records and will not attempt the A record fallback, making emails to such domains fail.
• Limited Deliverability Consequence for Sender: Sending to a domain that doesn't exist or isn't configured for email often results in a hard bounce, which, in isolation, doesn't severely impact the sender's reputation unless it's indicative of a broader pattern of poor list quality.
• List Quality Indicator: The presence of email addresses on domains without MX records in your list can be a strong indicator of other list hygiene issues (e.g., old data, problematic acquisition sources), which do affect deliverability.

Key considerations

• Thorough Validation: Employ robust email validation processes that not only check MX records but also attempt to connect to mail servers to confirm deliverability.
• DNS Query Specificity: When checking DNS, specify the MX record type in your dig or nslookup queries to avoid misinterpreting the presence of an A record as sufficient for email reception.
• Understanding RFCs: Familiarize yourself with RFCs like RFC 5321, which defines the Simple Mail Transfer Protocol (SMTP), to grasp the technical underpinnings of email routing.
• Proactive Monitoring: Implement tools to monitor DNS records for your sending domains and critical recipient domains, ensuring correct configurations.

Key findings

• RFC 5321 Standard: The core SMTP standard (RFC 5321) clearly states that if a DNS query for MX records returns an empty list, the domain should be treated as if it has an implicit MX record with a preference of 0, pointing to the domain's A record.
• Mail Exchanger Role: An MX record's primary function is to specify the mail servers responsible for accepting email messages on behalf of a domain, indicating the preferred routing for email.
• A Record as Fallback: The presence of an A record is necessary for the RFC fallback to function. Without an A record, even the implicit MX rule cannot direct mail.
• Configuration Necessity: For a domain to reliably send and receive email, proper configuration of DNS records, including explicit MX records (and often SPF and DKIM), is standard practice and expected by most receiving mail servers.

Key considerations

• Standard Compliance: While RFC 5321 specifies a fallback, not all mail servers strictly adhere to every part of RFCs, and some may simply reject mail to domains without explicit MX records.
• Expected Behavior: Modern email ecosystems are built on the expectation of explicit MX records for mail reception. Relying solely on the A record fallback is not a robust or recommended setup for active email communication.
• Error Handling: Mail servers will return specific SMTP error messages, such as 550 Host Unknown or 550 No Such User, when they cannot resolve a domain's MX or A record for email delivery.
• Comprehensive DNS: Beyond MX records, domains sending email should have properly configured SPF and DKIM records for authentication, as well as a DMARC policy, all of which contribute to deliverability and sender trustworthiness.