Strategies and resources for blocking disposable email domains and problematic TLDs
Matthew Whittaker
Co-founder & CTO, Suped
Published 19 Jul 2025
Updated 19 Aug 2025
8 min read
Dealing with disposable email domains (DEDs) and problematic top-level domains (TLDs) is an ongoing challenge for anyone managing email lists, user sign-ups, or communication platforms. These types of email addresses are often used for malicious purposes, such as spam, fraud, or simply to bypass registration limits, impacting your data quality, increasing bounce rates, and potentially damaging your sender reputation.
Understanding disposable email domains and problematic TLDs
Disposable email domains, sometimes called burner or temporary email addresses, are designed for short-term use and often self-destruct after a set period. They allow users to receive emails without revealing their true email address, which can be useful for privacy, but is frequently abused. These domains are created en masse, often following predictable patterns or using specific TLDs (e.g., mailinator.com or guerrillamail.com). We commonly encounter these in our efforts to keep email ecosystems healthy.
Problematic TLDs, on the other hand, are top-level domains that disproportionately host spam, phishing, or other malicious activities. While a TLD like .com is generally trustworthy, certain new gTLDs (generic top-level domains) or older country-code TLDs (ccTLDs) become magnets for abuse due to lax registration policies, low cost, or a lack of enforcement against bad actors. Knowing which TLDs to avoid can significantly reduce the influx of low-quality or harmful sign-ups.
These aren't always easy to spot. Some disposable email services use seemingly legitimate domains or subdomains, making them harder to identify without a comprehensive blocklist (or blacklist). The landscape of problematic TLDs also shifts, with new ones emerging as popular choices for spammers. This dynamic nature means that effective blocking strategies require continuous monitoring and adaptation to new threats.
Identifying suspicious email domains involves more than just looking for obvious throwaway names. It often includes analyzing patterns, such as domains with random character strings or those that appear to be intentionally misspelled variations of legitimate domains, known as typo domains. This proactive approach helps in maintaining a clean and engaged user base.
Why blocking them is crucial
Blocking disposable email domains and problematic TLDs is not merely about preventing spam or reducing unwanted sign-ups. It's a critical aspect of maintaining your sender reputation, ensuring data quality, and protecting your systems from potential abuse. Each time you send an email to a DED, it contributes to your bounce rate, signaling to Internet Service Providers (ISPs) that your list quality may be low. High bounce rates can lead to your legitimate emails being flagged as spam, ultimately affecting your email deliverability.
Beyond deliverability, DEDs are frequently used to engage in fraudulent activities, such as creating multiple accounts for free trials, exploiting referral programs, or submitting fake leads. This directly impacts your business's resources and can skew analytics, making it difficult to gauge true user engagement or marketing campaign effectiveness. By blocking these domains, you are actively protecting your platform's integrity.
Moreover, problematic TLDs are often associated with phishing attempts and malware distribution. While your primary concern might be preventing incoming malicious emails, allowing registrations from such TLDs could inadvertently open doors for spammers to use your platform for their nefarious activities, further damaging your brand's reputation. A proactive approach to blocking these can prevent significant headaches down the line.
Ultimately, the goal is to cultivate a healthy email list and user base. A clean list ensures that your messages reach engaged recipients, improving open rates, click-through rates, and overall campaign performance. It also reduces the likelihood of being placed on an email blocklist (or blacklist), which can have severe consequences for your sending capabilities. Learning why emails go to spam often reveals that poor list hygiene is a primary factor.
Strategies for identification and blocking
Identifying and blocking these problematic domains and TLDs requires a multi-faceted approach. Relying solely on manual blacklisting is often a losing battle due to the sheer volume and rapid creation of new disposable domains. Automated solutions and comprehensive data sources are essential.
One effective strategy involves leveraging known lists of disposable email domains. These lists are continuously updated by various communities and services that track and compile DEDs. We have previously discussed where to find comprehensive lists that you can integrate into your signup or email validation processes. For example, open-source projects often maintain extensive lists, such as the one available on GitHub's disposable email domain repository, which can be incredibly useful.
When it comes to problematic TLDs, consulting reputation statistics from trusted sources is key. Organizations like Spamhaus provide statistics on TLDs with the highest rates of spam. These insights can help you decide which TLDs to explicitly block or flag for stricter validation. The impact of top-level domains on email deliverability is significant and should not be underestimated.
Beyond lists, implementing real-time email verification at the point of sign-up is a robust defense. This involves checking the email address for syntax, domain validity, and whether it belongs to a known disposable service, or if it's a spam trap. This immediate feedback prevents bad data from entering your system in the first place, improving the overall quality of your email list and user base from the outset. We outline strategies to prevent disposable email sign-ups in detail elsewhere.
Disposable Email Domains
These are temporary email addresses that are valid for a short period, designed to be used once and then discarded. They often bypass normal email validation processes due to their transient nature.
Purpose: Avoid spam, bypass signup limits, test services.
Identification: Recognized by specific domain names (e.g., temp-mail.org), often found in public lists.
Impact: High bounce rates, inflated user counts, resource waste, potential for abuse.
Problematic TLDs
These are top-level domains that are frequently used by spammers, phishers, and other malicious actors due to factors like low registration costs or lax regulatory oversight.
Once you've identified the types of domains and TLDs you want to block, the next step is to implement effective mechanisms. The specific implementation will vary depending on your system, whether it's an email marketing platform, a web application for user sign-ups, or an internal email server.
For web forms and user registration, you can implement server-side validation that checks incoming email addresses against your blocklist (or blacklist). This can be done by maintaining a list of blocked domains and TLDs in a database or a configuration file. When a user submits a form, the email domain is checked against this list, and if a match is found, the submission is rejected. This is a fundamental step in how to accurately verify your email list.
Here's a simplified example of how you might set up a domain blocking list in a web application context, often stored in a configuration or a database. When a user attempts to sign up, the domain of their email address is checked against this list. We generally use a similar approach in many contexts, including our own efforts to help users with their email blacklist problems.
Example Python script for domain blockingpython
blocked_domains = [
"mailinator.com",
"temp-mail.org",
"yopmail.com",
"guerrillamail.com",
"*.ml",
"*.cf",
"*.ga"
]
def is_domain_blocked(email_address, blocked_list):
domain = email_address.split('@')[-1]
for blocked_item in blocked_list:
if blocked_item.startswith("*"):
tld = domain.split('.')[-1]
if tld == blocked_item[2:]:
return True
elif domain == blocked_item:
return True
return False
# Example usage:
# user_email = "test@mailinator.com"
# if is_domain_blocked(user_email, blocked_domains):
# print("Email domain is blocked.")
For email delivery systems, you can configure your Mail Transfer Agent (MTA) or email service provider to reject emails originating from or destined for these blocked domains and TLDs. This is often done through rules or filters that check the sender or recipient domain against a pre-defined list. Some email service providers offer built-in features for this, while others might require custom configurations or integrations with third-party email validation services that handle real-time checking against extensive DED lists and problematic TLDs. Remember that there are different types of email blocklists and choosing the right one for your specific needs is important.
Views from the trenches
Best practices
Leverage continually updated lists of disposable email domains for effective blocking.
Employ real-time email verification to identify and reject problematic addresses at entry.
Monitor signup and engagement data for unusual patterns or spikes from specific domains.
Educate your team on the importance of maintaining a clean email list for sender reputation.
Common pitfalls
Relying solely on manual blocklisting, which quickly becomes outdated and inefficient.
Being overly aggressive with TLD blocks, potentially blocking legitimate users mistakenly.
Ignoring underlying reasons for high volumes of disposable sign-ups, like poor form security.
Failing to regularly update blocking mechanisms, leaving systems vulnerable to new tactics.
Expert tips
Consider a tiered blocking approach, where certain TLDs are soft-blocked for review.
Integrate DED blocking with other security measures such as IP reputation checks.
Use a combination of general DED lists and specific domain-level blocking for observed threats.
Regularly analyze deliverability reports to identify unexpected bounces tied to specific domains.
Expert view
Using a comprehensive master list of disposable email domains can significantly simplify the process of blocking fraudulent sign-ups, especially for preventing whack-a-mole scenarios.
2018-11-20 - Email Geeks
Expert view
Implementing CAPTCHA solutions can effectively prevent an overwhelming volume of spam submissions and protect forms from getting hammered by malicious actors.
2018-11-20 - Email Geeks
Maintaining email list integrity
Effectively managing disposable email domains and problematic TLDs is a continuous effort. It requires a combination of robust technical solutions, reliance on up-to-date data, and a commitment to maintaining your email list quality. By implementing the right strategies, you can significantly reduce spam and fraud, protect your sender reputation, and ensure that your communications reach genuine, engaged recipients.
