How can I bulk check and clean MX records for a list of domains?

Key findings

• Command-line tools: Utilities like dig (Domain Information Groper) are powerful for bulk MX record lookups, especially when scripted.
• Scripting capability: For large lists (500+ domains), scripting the dig command or similar tools allows for efficient processing and output to formats like CSV for easier review.
• Email validation services: While potentially more costly, dedicated email verification tools offer comprehensive checks, including MX record validation, and can streamline the cleaning process.
• Null MX records: Some domains use a null MX record (MX record pointing to ".") to explicitly state they do not accept email, which should also be identified and removed.
• A record fallback: Senders are technically not required to have an MX record to receive email, as mail servers can fall back to the A record to attempt delivery. However, for deliverability, a properly configured MX record is preferred.

Key considerations

• Cost efficiency: Performing initial MX record checks in-house using command-line tools can significantly reduce the cost of subsequent, more thorough email validation services.
• Output parsing: The raw output from dig needs to be parsed effectively to identify domains with missing, invalid, or null MX records, often by directing the output to a CSV file.
• Categorization: Develop categories for domains that do not accept mail, such as dot MX, null MX, and domains that host parked pages, to ensure comprehensive cleaning. For more details on this, consider our guide on how to maintain a clean email list.
• System access: Access to a Linux, Mac, or Windows terminal with Bash is necessary to run command-line tools for bulk lookups.

Key opinions

• Pre-validation cleaning: Marketers often aim to conduct preliminary cleaning steps, such as checking for valid MX records, before sending their lists to professional email validation services. This reduces the number of addresses processed, thereby lowering costs.
• Manual script preference: Some marketers prefer using their own scripts or database extensions for MX lookups, providing more control and potentially greater cost savings compared to external tools for basic checks.
• Automation for efficiency: The need for bulk processing of domains (e.g., 500+) drives the search for automated solutions, whether via command-line scripting or specialized tools, to avoid manual, time-consuming checks.
• Impact on deliverability: Domains without valid MX records are understood to result in bounces, directly impacting sender reputation and deliverability rates. Cleaning these is a direct step towards improving email deliverability.

Key considerations

• Resource allocation: Balancing the upfront effort of building custom scripts versus the recurring cost of third-party validation services is a common decision point for marketers. Explore different affordable email verification tools.
• Data parsing complexity: Large datasets of domains can contain extraneous information, making parsing and extracting clean domain names a challenge before MX lookup.
• Comprehensive cleaning: Cleaning extends beyond just missing MX records to include null MX (domains not accepting mail) and parked domains that do not receive email.
• Scalability: The chosen method must be scalable to handle lists containing hundreds of thousands or even millions of domains, as discussed on Quora regarding large email lists.

Key opinions

• Command-line efficiency: Experts widely recommend dig as the quickest and easiest way to check MX records, especially when working with bulk lists.
• Scripting for scale: Scripting dig or similar tools is cited as an effective solution for processing large volumes of domains and generating reviewable output, like CSV files.
• MX record flexibility: It's important to understand that while generally expected, a domain is not technically required to have an MX record to receive email; mail servers can fall back to the A record.
• Identifying non-mail domains: Beyond just missing MX, experts advise checking for null MX records, which explicitly signal that a domain does not accept mail. This helps in categorizing MX records.

Key considerations

• Output readability: When scripting dig, using options like +noall +answer +cmd provides more useful context (the queried domain) than just +short, making the resulting file more practical for analysis.
• Custom script development: Developing a custom script, for example in PowerShell as suggested by a Medium article, allows for comprehensive checks including MX, SPF, and DMARC records, and can be tailored to specific output needs (e.g., CSV).
• Platform compatibility: While dig is native to Unix-like systems, its functionality (or similar tools) is increasingly available on Windows through Bash or PowerShell, making it accessible to a wider audience. For additional help on identifying suspicious MX records, see our related article.
• Avoiding extraneous data: The input file for bulk checks should be clean, with one domain per line, to prevent issues with parsing extraneous information within the domain list.

Key findings

• MX record function: MX records (Mail Exchanger records) are a type of DNS record that specifies which mail servers are responsible for accepting email messages on behalf of a domain name.
• Null MX definition: RFC 7505 defines a Null MX record as an intentional signal that a domain does not accept email, typically used for domains that are solely for web hosting or other purposes.
• DNS lookup tools: Tools like online MX lookup tools allow users to quickly check MX records for a given domain and verify email server responsiveness.
• Bulk checking with PowerShell: PowerShell cmdlets, such as Resolve-DnsName, can be used to query MX records for multiple domain names simultaneously, as documented by Practical 365.

Key considerations

• Preventing bounces: Properly identifying domains without valid MX records or with null MX is crucial to prevent email bounces and maintain a good sender reputation.
• DNS zone configuration: Each domain requires its own MX record in its public DNS zone for proper email routing, and existing records may need to be managed during setup.
• Email flow: MX records are fundamental to the flow of email across the internet, directing incoming messages to the correct mail servers. For advanced routing strategies, consider load balancing with MX records.
• API integration: Email validation APIs provide a programmatic way to check email lists, including MX record validity, integrating seamlessly with existing systems for automated cleaning. This is touched upon by Mailgun in their blog.