How do email list cleaning companies clean millions of emails daily and avoid being blocked?

10 Marketer opinions 6 Expert opinions 3 Technical articles 2 Resources

Summary

Email list cleaning companies employ a multifaceted approach to validate email addresses at scale while minimizing the risk of being blocked by ISPs and spam filters. These techniques range from passive methods like cross-referencing against databases of known spam traps, syntax checks, domain verification, and honeypot detection, to active methods such as SMTP connection testing, silent pings, and bounce verification analysis. To avoid overwhelming mail servers, they distribute validation requests across multiple IPs and throttle connection rates. Some experts question the legitimacy and effectiveness of some list cleaning companies, emphasizing the importance of proactive list hygiene practices like double opt-in and focusing on clean acquisition methods. The effectiveness of list cleaning also depends heavily on the list's source and age.

Key findings

Multiple Validation Techniques: List cleaning companies use a combination of passive and active techniques including syntax checks, domain verification, SMTP connection tests, honeypot detection, and cross-referencing against spam trap databases.
Scalability Measures: To handle millions of emails daily without being blocked, they distribute validation requests across numerous IPs and throttle connection rates to avoid overwhelming mail servers.
Proactive Hygiene Emphasis: Experts emphasize the importance of proactive list hygiene through methods like double opt-in, which ensures addresses are valid from the start and minimizes the need for extensive cleaning.
Alternative Data Methods: Some more modern techniques like SMTP greylisting provide ways to verify if an email is legitimate without the risk of being marked as spam.
Effectiveness Limitations: List cleaning is most effective for current customers or recent opt-ins and less effective for purchased lists or older data, which may contain a high percentage of invalid or abandoned addresses.
Real-time Verification Methods: List cleaning companies are using real-time verification methods like role-based account detection, disposable email detection, and typo correction to ensure that an email address is legitimate without issues.

Key considerations

Legitimacy Verification: Carefully evaluate the legitimacy and reputation of list cleaning providers, as some may engage in questionable practices or provide limited effectiveness.
Acquisition Practices: Prioritize clean email acquisition methods (double opt-in, clear value proposition, typo correction) to minimize the need for extensive cleaning and improve overall list quality.
List Segmentation: Segment email lists based on source and age to tailor cleaning efforts and prioritize the most valuable and receptive contacts.
Bounce Handling: Implement robust bounce handling procedures and remove invalid addresses promptly to maintain a healthy sender reputation.
Risk Assessment: Carefully assess the potential risks and benefits of different list cleaning techniques and select methods that align with your specific needs and goals.

What email marketers say
10Marketer opinions

Email list cleaning companies employ a variety of techniques to validate email addresses while minimizing the risk of being blocked. These methods range from passive approaches like cross-referencing against databases of known spam traps and invalid addresses, to active techniques such as syntax checks, domain verification, and SMTP connection tests. They often use data analytics, spread validation requests across multiple IPs, throttle connection rates, and monitor blacklists. More advanced techniques involve greylisting, bounce verification analysis, and 'silent pings' that predict deliverability without triggering spam traps. The double opt-in method during the subscription process ensures email addresses are valid from the start.

Key opinions

Data Analytics: Many list cleaning services use data analytics on their entire data set to determine the probability of an address being valid, moving away from solely relying on direct delivery attempts.
Syntax and Domain Checks: Basic checks like syntax verification, domain existence confirmation, and identifying role-based addresses are common first steps in the cleaning process.
SMTP Connection Tests: Email validation services often connect to mail servers to simulate sending a message and verify the mailbox's existence without actually sending an email.
IP Rotation and Throttling: To avoid overwhelming mail servers, list cleaning companies spread validation requests across numerous IPs and throttle their connection rates.
Spam Trap Databases: Some services maintain and cross-reference lists against databases of known spam traps and invalid addresses to passively identify and remove risky emails.
Bounce Verification: Analysing the mail servers responses provides a way of cleaning the emails without the email counting as spam or getting blocked.

Key considerations

Effectiveness: List cleaning is most effective for current customer lists or recent opt-ins, and less effective for purchased lists or older data.
Blacklist Monitoring: Reputable list cleaning services should monitor blacklists and adjust their sending behavior to avoid being listed.
Double Opt-in: Implementing a double opt-in process during subscription helps ensure the initial validity of email addresses.
Greylisting: Temporary failing emails is one way to verify the email without the risk of being flagged as spam, so ensure this is set up.

Marketer view

Email marketer from LinkedIn answers that cleaning an email list is an automated procedure. Using sophisticated software, list cleaning companies employ a variety of approaches. One tactic is to perform a syntax check and fix any faults (for example, taking out spaces and special characters). Other tactics check to see if a legitimate MX record exists for the domain.

November 2024 - LinkedIn

Marketer view

Email marketer from NeverBounce.com explains that one way email list cleaning companies clean millions of emails daily is through their Bounce Verification technology. It analyzes a mail server's response and determines whether or not it is bouncing. With this the software doesn't count as spam or being blocked.

February 2023 - NeverBounce.com

Marketer view

Email marketer from Reddit explains that some list cleaning services maintain large databases of known spam traps and invalid addresses. They cross-reference submitted lists against these databases to identify and remove risky emails. This is a passive technique that doesn't involve sending any emails, reducing the risk of being blocked.

March 2023 - Reddit

Marketer view

Email marketer from EmailStuff forum shares Email list cleaning companies use a combination of techniques. This includes Syntax Verification and SMTP Verification to prevent any risk of being blocked. This can quickly get rid of emails from the list.

March 2022 - EmailStuff Forum

Marketer view

Email marketer from StackExchange responds that Email List Cleaning companies also use greylisting and temporary failures. This means they will temporarily fail the emails on the first connection to verify it's a real server and not a bot. This allows them to verify an email without the risk of it being flagged as spam.

February 2024 - StackExchange

Marketer view

Email marketer from Validity.com explains that email list cleaning companies use various methods including syntax checks to identify malformed addresses, domain checks to ensure the domain exists and is active, and role-based address detection to flag generic addresses like sales@ or info@ that may be problematic. They also use honeypot detection to identify addresses that are only used to catch spammers.

March 2021 - Validity.com

Marketer view

Email marketer from EmailHippo.com responds that to avoid being blocked, list cleaning companies spread their validation requests across numerous IPs and throttle their connection rates to avoid overwhelming mail servers and triggering abuse detection systems. They also monitor blacklists and adjust their sending behavior accordingly.

April 2024 - EmailHippo.com

Marketer view

Email marketer from Email Geeks shares that in the early days list cleaning companies tried to deliver to the addresses and then drop the connection once the recipient was accepted, but that got them blocked frequently. So most of them these days use data analytics on their entire data set to work out the probability of an address being valid. It's a pretty murky world, full of scammers and data theft, and not legal in every jurisdiction.

December 2024 - Email Geeks

Marketer view

Email marketer from Medium explains a simple technique for ensuring that recipients provided you with accurate email addresses: double opt-in. That is, individuals can register for your email list on one form, but you must send them a confirmation email asking them to validate their email address before they can join.

May 2021 - Medium

Marketer view

Email marketer from ZeroBounce.net shares that email validation services connect to mail servers to verify the existence of mailboxes without sending an actual email. This involves checking the SMTP connection and simulating sending a message to see if the server accepts it. If the server rejects the connection, it's an invalid email. This is done at scale to clean millions of addresses daily.

March 2023 - ZeroBounce.net

What the experts say
6Expert opinions

Experts generally express skepticism about the effectiveness and legitimacy of list cleaning companies. Some suggest they lie about their effectiveness or simply resell bounced addresses. Those employing SMTP tickling often get blocked due to spam-like traffic. A proactive approach to list hygiene, focusing on acquisition methods (double entry, clear value proposition, typo correction) is preferred. Kickbox is highlighted as a recommended validation service. List cleaning effectiveness varies based on the list source and age, being most useful for current customers or recent opt-ins, and ineffective for purchased or old lists. Sending 'pings' to validate addresses can also lead to blocking if not done carefully.

Key opinions

Legitimacy Concerns: Some experts question the legitimacy of many list cleaning companies, suggesting deceptive practices.
Acquisition Focus: Prioritizing clean acquisition methods (double opt-in, clear value) is considered superior to reactive list cleaning.
Limited Effectiveness: List cleaning's effectiveness depends heavily on the list's source and age; it doesn't 'fix' purchased or old lists.
Blocking Risks: SMTP tickling and sending 'pings' to validate addresses can lead to blocking due to spam-like behavior.
Kickbox Recommendation: Kickbox is specifically recommended by some experts as a reliable validation service.

Key considerations

List Source & Age: Assess the origin and age of your list to determine if cleaning will be effective; purchased or old lists are unlikely to benefit.
Acquisition Methods: Review and improve your email acquisition processes to minimize the need for cleaning in the first place.
Reputation: Be cautious when selecting a list cleaning service, as some engage in questionable practices.
Alternative tools: Consider using Kickbox as it has a good philosophy and anti-abuse approach.

Expert view

Expert from Email Geeks answers that the list cleaning companies that do SMTP tickling do get blocked. One approached her around a decade ago to help them bypass filters, their system at that time was to basically snowshoe IPs and domains to try and avoid the blocks that the ISPs put up.

February 2022 - Email Geeks

Expert view

Expert from Email Geeks explains that there are no legitimate “list cleaning companies”, so the first approach is just to lie about their effectiveness. The next is to acquire lists of addresses that bounce and more legitimate services buy or trade data about whether an email address delivers from other senders. There are still bottom of the barrel scam companies that do test via attempted delivery, I’m sure, but the accuracy of that is terrible because they get blocked which means that valid email addresses bounce when they try and deliver to them.

July 2021 - Email Geeks

Expert view

Expert from Email Geeks explains list hygiene is trying to bandage the wound and you're better served trying to avoid getting wounded in the first place by focusing on acquisition through things like double entry email, clear value to customer and corrections on typos in forms and that if you have done all that and still want to do some validation on your audience, my vote is for Kickbox.

June 2023 - Email Geeks

Expert view

Expert from Email Geeks recommends kickbox, being the only player in the space that she will recommend and that’s after Jack spent a lot of time talking to me about their philosophy and anti-abuse approach.

September 2023 - Email Geeks

Expert view

Expert from Spam Resource explains that list cleaning effectiveness varies. It depends a great deal on the source of your list and how long you've had it. Cleaning does not fix a purchased list, or a list that's more than a year old. List cleaning is really most useful if you have a list of current customers or recent opt-ins from your website.

June 2021 - Spam Resource

Expert view

Expert from Word to the Wise responds that one of the reasons email list cleaning companies get blocked is that they are generating traffic that looks like spam. One of the common ways they validate an email address is by sending a ping which is a basic network utility. A ping sends a small packet of data to a specific IP address and requests a response. If the target IP address is active, it will send a reply back to the source IP address. However, the target IP address can prevent any risks of being spammed by not responding.

October 2024 - Word to the Wise

What the documentation says
3Technical articles

Email list cleaning services employ various techniques to verify email addresses without triggering spam traps and getting blocked. These include sending 'silent pings', utilizing sophisticated algorithms to predict deliverability, real-time email verification using role-based account detection, disposable email detection, typo correction, and checking domain name records to ensure the domain exists and is active.

Key findings

Silent Pings and Algorithms: List hygiene services often verify email addresses by sending a 'silent ping' or using sophisticated algorithms to predict deliverability without sending an email.
Real-Time Email Verification: Real-time email verification uses sophisticated techniques such as role-based account detection, disposable email detection, and typo correction to determine whether an email address is valid.
Domain Name Record Checks: Email verification tools check the DNS records of the domain name to ensure the domain exists and is active.

Key considerations

Algorithm Accuracy: It's important to understand the accuracy of algorithms used to predict deliverability.
Real-Time Implications: Understanding the implications of real-time email verification and make sure you select the correct option.
DNS Record Information: Make sure that DNS records are accurate and up to date.

Technical article

Documentation from Mailgun shares that real-time email verification uses sophisticated techniques such as role-based account detection, disposable email detection, and typo correction to determine whether an email address is valid. By using these techniques, they do not have to send emails and therefore prevent issues.

July 2024 - Mailgun

Technical article

Documentation from Kickbox explains that Email Verification tools look at the domain name of an email for example @gmail.com, and check the DNS records to ensure the domain exits and is active. This can quickly detect invalid or parked domains, and prevent being blocked.

June 2022 - Kickbox.com

Technical article

Documentation from SparkPost explains that list hygiene services often verify email addresses by sending a 'silent ping' or using sophisticated algorithms to predict deliverability without actually sending an email that could trigger spam traps. This minimizes the risk of being blocked while still identifying invalid or risky addresses.

April 2024 - SparkPost