How can I filter and sanitize a large list of email domains using DNS and other techniques?
Summary
What email marketers say9Marketer opinions
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.
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.
Email marketer from Email Hippo answers that email validation tools verify that an email address exists, can receive mail, and is not a disposable or role-based address. This helps in identifying valid and active email addresses.
Email marketer from Reddit shares that checking for valid MX records is a basic but important step. Domains without MX records are unlikely to send or receive emails and can be filtered out.
Email marketer from Email Marketing Forum shares that maintaining a list of common disposable email domain names (e.g., mailinator.com, tempmail.com) and filtering them out is a good practice to remove temporary or fake email addresses.
Email marketer from Debounce explains tracking and removing email addresses that result in hard bounces is crucial for maintaining a clean email list. Hard bounces indicate permanent delivery failures.
Email marketer from StackOverflow explains Regular expressions can be used to sanitize email addresses by removing invalid characters and standardizing the format. It can also be used to identify common spam patterns.
Marketer from Email Geeks shares that companies usually have developers and admins who know DNS at a basic level and can run a dirty script to filter the domain list, then spreadsheet the results.
Email marketer from EmailListVerify explains that performing syntax validation to ensure email addresses conform to the standard format (e.g., local-part@domain) helps remove invalid email addresses.
What the experts say5Expert opinions
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.
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.
Expert from Email Geeks states she needs a list of all domains in the database to run DNS work and see what she can find out, also that localhost, no mx, dotmx, parked domains and (none) are all different classifications they’ve put into this over the years. There’s also a servfail and nxdomain.
Expert from Word to the Wise explains that utilizing DNSBLs (DNS-based Blackhole Lists) is a valuable method for filtering email domains. These lists contain domains and IP addresses known for spamming activities, and querying against them helps identify potentially harmful domains within your list.
Expert from Spamresource shares using a technique called greylisting, temporarily rejecting emails from unknown senders. Legitimate servers will retry sending, while spammers often don't, thus filtering out many unwanted messages.
What the documentation says5Technical articles
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.
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.
Documentation from Spamhaus shares that they maintain several blocklists based on domain reputation, which can be used to filter domains known for spam or malicious activities.
Documentation from AbuseIPDB shares that checking the IP reputation of the sending server can help identify potential spammers. Blocklists like AbuseIPDB maintain lists of IPs associated with malicious activity.
Documentation from DNSFilter explains they provides DNS-based content filtering and threat protection, allowing organizations to block access to malicious or inappropriate domains.