Cold Email, Domain Warming, & Their Impact on the Email Ecosystem
Cold Email, Domain Warming, & Their Impact on the Email Ecosystem
Cold email outreach is a business practice used by sales, promotion, and other operations. Many think cold email is harmless lead generation approach. However, despite the intentions, without confirmed opt-in, cold email is ultimately another form of unsolicited messages (spam). The use of AI has increased cold emailers ability to quickly generate and distribute new content and domains.
What is Cold Email? Is it Spam?
Cold email outreach is an approach that otherwise legitimate businesses can use for sales and promotion. They’re commonly used for sales and lead generation, job hunting, networking, or collaboration. While the senders may claim personalization and “interest”, cold emails are sent without the receiver’s consent.
As Spamhaus put it, “Cold emailing, as it’s practiced today, is spam — for inboxes, businesses, and the internet… By definition, there is no difference between cold email and spam – no consent, no commercial relationship, and often some form of bulk (automated) delivery.”
Messages are considered spam when they are used to blast massive volumes to unverified lists (or unconfirmed recipients) while evading detection, using hidden networks and rotating disposable domains. Cold email spam is often untargeted and random, uses generic templates, and includes deceptive links. Additionally, they violate the law by using fake sender identities and hiding the source of the transmission.
Cold Email's Attempt to Evade Filters
A cold email is an outreach tactic where a sender distributes a high volume of unsolicited messages across a wide network. Similar to “snowshoe spamming” and spreading sending across multiple IPs, cold email will quickly cycle through domains, so that no single domain appears large enough to trigger anti-spam filters.
By spreading message volume over a large number of distinct channels (in the way that snowshoes distribute body weight across a large surface area), traditional security filters fail to associate any single message with the heavy total volume.
Per the research team at SURBL, actors often send less than 10 emails using one domain, before switching to the next related domain to avoid detection The SURBL research teams reports seeing 20x more domains related to cold email compared to last year.
What is Domain Warming?
Organizations that rely on maximizing inbox placement face operational challenges with spam filters. When an organization provisions new IP addresses, it faces a cold-start problem. Mail Receiver Systems like Google Workspace and Microsoft 365 use historical data to calculate trust scores. A sudden influx of high-volume mail from an unrated source triggers immediate rate-limiting or spam folder placement to mitigate risk.
These organizations use a technique called domain warming to gradually increase the volume of emails sent from new domains to build positive sender reputations with mailbox providers.
M3AAWG best practices recommend start low and slow for domain warm-up and to increase sending volume slowly (consider 6 weeks of warm-up as an average). The idea is to target recipients in a way that is personalized and builds trust.
However, many “domain warming services” engage in unethical email behavior to create artificial reputation.
How is Domain Warming Abused?
Artificial domain warming is the unethical practice of using automated services and networks of fake accounts to manufacture positive email engagement. This practice is also utilized by spammers. Instead of earning a sender reputation naturally through real subscribers, spammers use these tactics to convince mail providers that their domains are trustworthy.
This manipulation is typically used by bad actors or aggressive cold-outreach marketers to bypass spam filters and rapidly scale massive, unsolicited email campaigns. They loop fake interactions with manufactured networks that control thousands of dummy or compromised email accounts to exchange messages with each other, mark the emails as read, click links, and generate prewritten replies. Mailbox providers observe this activity as a legitimate and highly engaged audience, which artificially inflates the sender’s domain reputation.
What are the Risks?
Deceptive domain warming services are used to build and maintain artificial trust with mailbox providers. Gaming the trust metrics of mail providers fundamentally corrupts the email ecosystem. When senders bypass authentic list-building and use bots to simulate high engagement, it causes broad operational and financial harm.
In addition to cluttering mailboxes with spam, recipients are exposed to phishing and financial scams. Deceptive warming is highly favored by malicious threat actors, and manufacturing clean domain histories allows attackers to deliver phishing lures, malware links, and credential harvesting tools directly into primary folders. This degrades trust over time, clogs communication, and fatigues users to a degree that they begin to doubt the legitimacy of critical and authenticated communications.
As legitimate brands conduct business with similar, but distinct legal and ethical practices, the lines begin to blur between outreach and spam. This association with unethical bot-driven spam permanently erodes customer confidence and drives down revenue. Overcoming that kind of burnout requires high recovery costs and sometimes a replacement of the entire domain space.
Proactive Prevention with SURBL
The SURBL team has been working diligently to identify domains related to these cold email and domain warming practices.
They’ve found actors register thousands of domains to avoid detection. The team suspects the use of AI to rapidly create similar domains, related to the brand and industry.
These domains are added to SURBL MULTI, under its Abuse sublist. Their Abuse sublist has grown 48% in the last 12 months.
The good news is – SURBL datasets can be used by email senders and providers to identify and prevent cold email.
Conclusion
Email works when recipients trust senders. When reputation is manufactured instead of earned, the whole ecosystem suffers. Senders who play fair lose, and mailbox providers are forced to raise security guardrails in a way that impacts everyone.
SURBL and the broader security community remain committed to maintaining a clean, predictable, and secure ecosystem for global communications. The usage of automated inbox warming networks presents an unacceptable security anomaly that actively undermines threat intelligence reporting.
Cold Email, Domain Warming, & Their Impact on the Email Ecosystem
Cold email outreach is a business practice used by sales, promotion, and other operations. Many think cold email is harmless lead generation approach. However, despite the intentions, without confirmed opt-in, cold email is ultimately another form of unsolicited messages (spam). The use of AI has increased cold emailers ability to quickly generate and distribute new content and domains.
What is Cold Email? Is it Spam?
Cold email outreach is an approach that otherwise legitimate businesses can use for sales and promotion. They’re commonly used for sales and lead generation, job hunting, networking, or collaboration. While the senders may claim personalization and “interest”, cold emails are sent without the receiver’s consent.
As Spamhaus put it, “Cold emailing, as it’s practiced today, is spam — for inboxes, businesses, and the internet… By definition, there is no difference between cold email and spam – no consent, no commercial relationship, and often some form of bulk (automated) delivery.”
Messages are considered spam when they are used to blast massive volumes to unverified lists (or unconfirmed recipients) while evading detection, using hidden networks and rotating disposable domains. Cold email spam is often untargeted and random, uses generic templates, and includes deceptive links. Additionally, they violate the law by using fake sender identities and hiding the source of the transmission.
Cold Email's Attempt to Evade Filters
A cold email is an outreach tactic where a sender distributes a high volume of unsolicited messages across a wide network. Similar to “snowshoe spamming” and spreading sending across multiple IPs, cold email will quickly cycle through domains, so that no single domain appears large enough to trigger anti-spam filters.
By spreading message volume over a large number of distinct channels (in the way that snowshoes distribute body weight across a large surface area), traditional security filters fail to associate any single message with the heavy total volume.
Per the research team at SURBL, actors often send less than 10 emails using one domain, before switching to the next related domain to avoid detection The SURBL research teams reports seeing 20x more domains related to cold email compared to last year.
What is Domain Warming?
Organizations that rely on maximizing inbox placement face operational challenges with spam filters. When an organization provisions new IP addresses, it faces a cold-start problem. Mail Receiver Systems like Google Workspace and Microsoft 365 use historical data to calculate trust scores. A sudden influx of high-volume mail from an unrated source triggers immediate rate-limiting or spam folder placement to mitigate risk.
These organizations use a technique called domain warming to gradually increase the volume of emails sent from new domains to build positive sender reputations with mailbox providers.
M3AAWG best practices recommend start low and slow for domain warm-up and to increase sending volume slowly (consider 6 weeks of warm-up as an average). The idea is to target recipients in a way that is personalized and builds trust.
However, many “domain warming services” engage in unethical email behavior to create artificial reputation.
How is Domain Warming Abused?
Artificial domain warming is the unethical practice of using automated services and networks of fake accounts to manufacture positive email engagement. This practice is also utilized by spammers. Instead of earning a sender reputation naturally through real subscribers, spammers use these tactics to convince mail providers that their domains are trustworthy.
This manipulation is typically used by bad actors or aggressive cold-outreach marketers to bypass spam filters and rapidly scale massive, unsolicited email campaigns. They loop fake interactions with manufactured networks that control thousands of dummy or compromised email accounts to exchange messages with each other, mark the emails as read, click links, and generate prewritten replies. Mailbox providers observe this activity as a legitimate and highly engaged audience, which artificially inflates the sender’s domain reputation.
What are the Risks?
Deceptive domain warming services are used to build and maintain artificial trust with mailbox providers. Gaming the trust metrics of mail providers fundamentally corrupts the email ecosystem. When senders bypass authentic list-building and use bots to simulate high engagement, it causes broad operational and financial harm.
In addition to cluttering mailboxes with spam, recipients are exposed to phishing and financial scams. Deceptive warming is highly favored by malicious threat actors, and manufacturing clean domain histories allows attackers to deliver phishing lures, malware links, and credential harvesting tools directly into primary folders. This degrades trust over time, clogs communication, and fatigues users to a degree that they begin to doubt the legitimacy of critical and authenticated communications.
As legitimate brands conduct business with similar, but distinct legal and ethical practices, the lines begin to blur between outreach and spam. This association with unethical bot-driven spam permanently erodes customer confidence and drives down revenue. Overcoming that kind of burnout requires high recovery costs and sometimes a replacement of the entire domain space.
Proactive Prevention with SURBL
The SURBL team has been working diligently to identify domains related to these cold email and domain warming practices.
They’ve found actors register thousands of domains to avoid detection. The team suspects the use of AI to rapidly create similar domains, related to the brand and industry.
These domains are added to SURBL MULTI, under its Abuse sublist. Their Abuse sublist has grown 48% in the last 12 months.
The good news is – SURBL datasets can be used by email senders and providers to identify and prevent cold email.
Conclusion
Email works when recipients trust senders. When reputation is manufactured instead of earned, the whole ecosystem suffers. Senders who play fair lose, and mailbox providers are forced to raise security guardrails in a way that impacts everyone.
SURBL and the broader security community remain committed to maintaining a clean, predictable, and secure ecosystem for global communications. The usage of automated inbox warming networks presents an unacceptable security anomaly that actively undermines threat intelligence reporting.
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