Are email warm-up tools like Warmy.io effective and legal?
Michael Ko
Co-founder & CEO, Suped
Published 11 May 2025
Updated 16 Aug 2025
6 min read
Email warm-up tools like Warmy.io have gained significant attention in the email marketing and cold outreach communities. The promise is enticing: quickly build a positive sender reputation for a new domain or IP address, ensuring your emails land in the inbox and bypass spam filters.
These services often claim to automate the process of simulating real human interaction with your emails, thereby tricking mailbox providers into trusting your sending practices. However, a deeper look reveals complexities regarding their actual effectiveness and, more critically, their adherence to legal and ethical email sending standards.
The mechanics of email warm-up tools
Email warm-up tools typically operate by connecting to your email account and sending emails to a network of other participating email addresses, often referred to as seed accounts. These seed accounts then perform actions such as opening your emails, replying to them, marking them as important, and moving them out of the spam folder. The idea is to create artificial engagement signals that mimic legitimate sending behavior over time.
The goal of this simulated activity is to build a positive sender reputation quickly, especially for new domains or those that have experienced deliverability issues. Without this initial warm-up phase, large volumes of email from new or cold domains might be flagged as spam by mailbox providers like Gmail, Google, Outlook, or Yahoo. It's a method intended to shortcut the natural process of building trust with email providers.
These tools automate what would otherwise be a tedious, manual process of gradually increasing sending volume and engagement. They often integrate with popular email services, allowing users to connect their existing inboxes and manage the warm-up process from a centralized dashboard. Some even claim to use AI to optimize the warming strategy.
Questionable effectiveness
The core question remains: are these tools actually effective in the long run? While they might provide a superficial boost to sender reputation initially, the consensus among deliverability experts is that their effectiveness is limited and often temporary. Mailbox providers are increasingly sophisticated in detecting artificial engagement. Their algorithms are designed to identify genuine human interaction versus automated, fabricated signals.
If caught, your domain or IP address could face severe penalties, including being added to a private blocklist (or blacklist), leading to persistent deliverability issues. As EmailChaser noted, "Trying to artificially manipulate your response rate with email warm-up tools is not effective, and will cause your emails to go to spam."
True sender reputation is built on consistent, legitimate sending to engaged recipients. This involves careful list hygiene, relevant content, and proper email authentication. Relying solely on artificial engagement can create a fragile reputation that collapses once real campaigns begin.
The problem with artificial warm-up
Detection Risk: Mailbox providers are constantly evolving their spam detection algorithms. Automated engagement patterns can be easily identified and flagged.
Temporary Effect: Any positive reputation gained through artificial means is likely to diminish rapidly once real sending begins, potentially leading to a sudden drop in deliverability.
False Sense of Security: Believing a warm-up tool has solved your deliverability issues can lead to neglecting essential best practices, ultimately harming your long-term success.
Legality and ethical considerations
The legality of email warm-up tools is a complex issue. While the act of sending emails to seed accounts for warming purposes may not be inherently illegal, the implications can quickly cross into problematic territory. For instance, if these services are used to send mass emails to actual mailing lists without adhering to consumer protection laws, it can lead to legal complications. Skrapp.io states that email warm-up is legal as long as it complies with regulations like CAN-SPAM, GDPR, and CASL, but emphasizes ethical warmup practices.
A common point of concern arises if the warm-up tool sends emails from your primary email account (like a Gmail or Google Workspace address) and these emails are part of a mass mailing campaign. Such campaigns are legally required to include an unsubscribe option and a physical address, which are frequently omitted by warm-up services aiming to simulate one-to-one communication. This omission can lead to direct violations of anti-spam laws.
Furthermore, from an ethical standpoint, attempting to trick mailbox providers can be seen as an unethical practice. It prioritizes short-term gains over building a genuine, trustworthy sender identity. This can damage your brand's reputation with legitimate users and lead to issues beyond just deliverability, such as being flagged as a sender of unsolicited email.
Artificial warm-up (e.g., Warmy.io)
Engagement: Relies on automated interactions from a network of seed accounts to simulate positive engagement signals like opens and replies.
Reputation Impact: Provides a superficial and often temporary boost to sender reputation, but risks detection and penalties from mailbox providers.
Compliance: May lead to legal issues if used for mass mailings that violate CAN-SPAM, GDPR, or CASL by omitting required elements like unsubscribes or physical addresses.
Organic warm-up (recommended)
Engagement: Focuses on sending to genuinely engaged subscribers who have opted into your communications. Builds trust naturally.
Reputation Impact: Cultivates a robust and lasting sender reputation recognized positively by mailbox providers, leading to consistent inbox placement.
Compliance: Inherently compliant by adhering to legal requirements, promoting ethical sending, and maintaining recipient trust.
Sustainable approaches to sender reputation
Instead of relying on questionable artificial methods, focus on building sender reputation through legitimate and sustainable practices. This approach not only ensures compliance but also fosters a healthy and long-term relationship with mailbox providers and your subscribers.
For new domains or IP addresses, a gradual warm-up plan is crucial. Start by sending small volumes of email to your most engaged subscribers and slowly increase the volume and audience size over several weeks. This natural progression signals to mailbox providers that you are a legitimate sender.
Implementing strong email authentication protocols like SPF, DKIM, and DMARC is also fundamental. These technical configurations verify that emails are indeed coming from your domain, preventing spoofing and significantly contributing to your sender reputation. Consistently monitoring your deliverability and domain reputation metrics will provide real-time insights into your sending health.
Views from the trenches
Best practices
Maintain a clean email list by regularly removing inactive or bounced addresses to improve deliverability.
Segment your audience and send targeted content to increase engagement and reduce spam complaints.
Monitor your sender reputation using tools like Google Postmaster Tools for key insights.
Ensure all emails include clear unsubscribe options to comply with anti-spam regulations.
Common pitfalls
Relying solely on automated warm-up services without genuine engagement strategies.
Ignoring mailbox provider feedback loops and treating spam complaints as insignificant.
Sending to unengaged or old lists immediately after a warm-up period, leading to reputation drops.
Failing to implement or properly configure email authentication protocols like DMARC.
Expert tips
Prioritize sending quality content that resonates with your audience to naturally boost engagement metrics.
Gradually increase your sending volume over time, starting with your most active subscribers.
Actively encourage recipients to add your email address to their contacts and move emails out of spam if they land there.
Invest in robust email infrastructure and reputable email service providers to support deliverability.
Marketer view
Marketer from Email Geeks says that mailbox providers disapprove of attempts to fake engagement and manipulate their reputation systems.
2022-12-15 - Email Geeks
Marketer view
Marketer from Email Geeks advises strongly against using warm-up tools.
2022-12-15 - Email Geeks
The path to lasting deliverability
While email warm-up tools like Warmy.io present an attractive shortcut to improving deliverability, their effectiveness is often overstated and their methods carry significant risks. Artificial engagement is increasingly detected by sophisticated mailbox providers, leading to potential blocklisting (or blacklisting) and long-term damage to your sender reputation.
The key to sustained email deliverability lies in ethical, consistent, and engagement-driven sending practices. Investing in proper authentication, gradual volume increases, and genuine audience interaction will yield far better and more reliable results than any quick-fix warm-up tool.
Google, 
Outlook, or 
Yahoo. It's a method intended to shortcut the natural process of building trust with email providers.
or Google Workspace address) and these emails are part of a mass mailing campaign. Such campaigns are legally required to include an unsubscribe option and a physical address, which are frequently omitted by warm-up services aiming to simulate one-to-one communication. This omission can lead to direct violations of anti-spam laws.
