Summary
Filtering and sanitizing a large email domain list involves a multi-faceted approach, combining DNS analysis, syntax validation, and reputation checks. Analyzing DNS records can identify various domain classifications (e.g., parked, invalid MX, localhost) and DNS errors (servfail, nxdomain). Syntax validation ensures addresses conform to RFC standards. Companies can leverage internal resources to script basic DNS filtering. Reputation blocklists (Spamhaus, AbuseIPDB) help identify spam domains and sending IPs. Email validation tools verify existence, activity, and prevent disposable/role-based addresses. SPF and DKIM authentication filters spoofed addresses. Greylisting temporarily rejects emails from unknown senders. DNS policies offer traffic redirection or blocking. Spam trap detection is crucial. Removing hard bounces, disposable domains, and role-based addresses improve deliverability. Finally, utilizing DNSBLs is effective for identifying spamming domains.
Key findings
- Comprehensive Filtering: Effective email domain sanitization requires a combination of DNS analysis, syntax validation, and reputation checks.
- DNS Record Analysis: Analyzing DNS records (MX, A, etc.) helps classify and identify problematic domains.
- Reputation-Based Blocking: Utilizing reputation blocklists (DNSBLs, IP-based lists) helps identify known spammers and malicious domains.
- Email Validation Tools: Email validation tools are effective for verifying email deliverability and preventing disposable/role-based addresses.
- RFC Compliance: Syntax validation is critical to removing invalid email addresses that do not comply with RFC standards.
Key considerations
- Resource Allocation: Determine whether to leverage internal development resources for custom filtering scripts or opt for commercial tools.
- Blocklist Accuracy: Carefully select reputable and regularly updated blocklists to minimize false positives.
- Authentication Implementation: Properly configure SPF and DKIM records for sending domains to improve authentication and deliverability.
- False Positive Mitigation: Implement monitoring and whitelisting to minimize the impact of false positives from filtering techniques.
- Ongoing Maintenance: Regularly update and maintain filtering rules, blocklists, and email validation processes to ensure continued effectiveness.
What email marketers say
9 marketer opinions
To filter and sanitize a large list of email domains, several techniques can be employed. Companies can leverage developers and admins to create scripts for DNS filtering and subsequent analysis. Validating MX records ensures domains can receive emails. Regular expressions can standardize formats and remove invalid characters. Email validation tools confirm email existence, activity, and type (non-disposable, non-role-based). Maintaining a list of disposable domains and removing them is crucial, as is syntax validation. Tracking and removing hard bounces, avoiding role-based emails, and employing spam trap detection services are essential steps for improving deliverability.
Key opinions
- DNS Filtering: Leveraging DNS filtering via internal scripts or external services can significantly reduce the number of invalid or harmful domains.
- Email Validation Tools: Email validation tools are effective at verifying the existence, activity, and type of email addresses.
- Syntax Validation: Syntax validation helps in ensuring email addresses conform to standard formats, eliminating malformed entries.
- Bounce Tracking: Tracking and removing hard bounces is crucial for maintaining a clean and effective email list.
- Spam Trap Detection: Using spam trap detection services can safeguard sender reputation and improve deliverability.
Key considerations
- Internal Resources: Consider leveraging internal developers and admins to create custom filtering scripts and workflows.
- Third-Party Tools: Explore and integrate third-party email validation and spam trap detection tools for more comprehensive cleaning.
- Disposable Domains: Maintain an updated list of disposable email domains to filter out temporary and fake addresses.
- Role-Based Addresses: Evaluate the impact of removing role-based addresses on your specific campaign goals and recipient engagement.
- Regular Maintenance: Email list sanitation is an ongoing process, requiring regular maintenance to maintain deliverability and sender reputation.
Marketer view
Email marketer from NeverBounce shares that removing role-based email addresses (e.g., sales@, info@) can improve deliverability as these addresses often have high bounce rates or are used for spam traps.
16 Dec 2022 - NeverBounce
Marketer view
Email marketer from ZeroBounce explains that using a service that can detect spam traps and remove them from your list is important to improve deliverability and protect sending reputation.
23 Sep 2022 - ZeroBounce
What the experts say
5 expert opinions
Sanitizing a large email domain list involves multiple layers of filtering and validation. Analyzing DNS records can identify various domain classifications like localhost, parked domains, and domains with DNS errors (servfail, nxdomain). Removing syntactically invalid addresses, those not conforming to RFC standards, is crucial. Greylisting, which temporarily rejects emails from unknown senders, helps filter out spammers. Lastly, utilizing DNSBLs is a beneficial technique for filtering email domains, as these lists contain domains and IP addresses known for spamming activities.
Key opinions
- DNS Analysis: Analyzing DNS records helps in classifying and identifying problematic domains (e.g., parked, invalid MX).
- Syntax Validation: Removing syntactically invalid email addresses is a fundamental step.
- Greylisting: Greylisting effectively filters out spammers by temporarily rejecting emails from unknown senders.
- DNSBL Utilization: DNSBLs are a reliable resource for identifying domains and IPs associated with spamming activity.
Key considerations
- Data Exploration: Thorough data exploration is necessary to determine which filters are most relevant to a specific data set.
- RFC Standards: Ensure all email addresses adhere to RFC standards for syntax to reduce invalid addresses.
- False Positives: When implementing greylisting, monitor for potential false positives and ensure legitimate servers retry sending.
- DNSBL Coverage: Choose DNSBLs that are reputable and regularly updated to ensure comprehensive coverage.
Expert view
Expert from Spamresource explains that removing syntactically invalid email addresses (those not conforming to RFC standards) is an essential first step in sanitizing a list. This includes checking for invalid characters, missing @ symbols, and malformed domain names.
30 Apr 2022 - Spamresource.com
Expert view
Expert from Email Geeks explains she is mostly doing this to see what filters are relevant, when they send me lots of data I often go through it.
23 Feb 2025 - Email Geeks
What the documentation says
5 technical articles
Filtering and sanitizing large email domain lists can be achieved through various DNS techniques. DNS policies, as highlighted by Microsoft Learn, allow blocking or redirecting traffic based on DNS queries. Spamhaus maintains reputation-based blocklists for identifying spam domains. IETF's documentation emphasizes the use of SPF and DKIM for authenticating email domains and filtering spoofed addresses. AbuseIPDB provides IP reputation checks to identify potential spammers. Finally, DNSFilter offers content filtering and threat protection by blocking access to malicious domains.
Key findings
- DNS Policies: DNS policies enable blocking or redirecting traffic based on DNS queries.
- Reputation Blocklists: Reputation-based blocklists (e.g., Spamhaus) effectively identify spam domains.
- Email Authentication: SPF and DKIM are DNS-based methods to verify domain authenticity and filter spoofed addresses.
- IP Reputation Checks: Checking IP reputation can help identify potential spammers.
- Content Filtering: DNS-based content filtering blocks access to malicious domains.
Key considerations
- Policy Implementation: Carefully configure DNS policies to avoid unintended blocking of legitimate traffic.
- Blocklist Selection: Choose reputable and regularly updated blocklists for accurate spam domain identification.
- Authentication Setup: Properly configure SPF and DKIM records for your sending domains to improve deliverability.
- IP Monitoring: Regularly monitor your sending IPs for potential listing on IP-based blocklists.
- Integration: Integrate DNS filtering with other email security measures for comprehensive protection.
Technical article
Documentation from IETF explains that SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) are DNS-based authentication methods that can be used to verify the authenticity of email domains and filter out spoofed addresses.
31 Aug 2024 - IETF
Technical article
Documentation from Microsoft Learn explains that DNS filtering can be implemented using DNS policies, allowing you to block or redirect traffic from specific domains based on DNS queries.
9 Feb 2022 - Microsoft Learn
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