What are IDN/Punycode domains and what does a screwed up Gmail authorization record look like?
Matthew Whittaker
Co-founder & CTO, Suped
Published 29 Jul 2025
Updated 17 Aug 2025
8 min read
As email increasingly integrates global languages and scripts, Internationalized Domain Names (IDNs) have emerged, allowing domain names to include characters beyond the basic ASCII set. This means domains can feature characters from various languages, like Arabic, Chinese, or Cyrillic. While this opens up the internet to a broader audience, it also introduces complexities and potential security risks.
One significant concern involves Punycode, the ASCII representation of IDNs. Punycode ensures that these international characters can be processed by the Domain Name System (DNS), which traditionally only handles ASCII characters. However, this conversion mechanism has become a tool for sophisticated phishing attacks. Beyond IDN complexities, even standard DNS records, like those for Gmail authorization, can be misconfigured, leading to severe deliverability issues and security vulnerabilities. Understanding these elements is crucial for maintaining robust email security and reliable deliverability.
Understanding IDN and Punycode
Internationalized Domain Names, or IDNs, enable the use of non-ASCII characters in domain names, encompassing a wide range of scripts and symbols from languages around the world. This was a crucial development to make the internet more accessible globally, moving beyond the limitations of the traditional Latin alphabet. For example, a domain could be bücher.com instead of buecher.com, allowing brands and individuals to use their native language characters.
However, the underlying DNS system was designed to handle only a limited set of ASCII characters. To bridge this gap, Punycode was introduced. Punycode is a special encoding syntax that converts Unicode characters into a sequence of ASCII characters, prefixed with xn--. This conversion allows IDNs to be resolved by existing DNS infrastructure. For instance, the IDN bücher.com would be converted to xn--bcher-kva.com for DNS resolution purposes. While essential for global internet use, this system introduces a new vector for phishing.
Punycode example of bücher.com
xn--bcher-kva.com
The main issue arises when malicious actors leverage the visual similarities between characters from different scripts to create deceptive domain names. This is known as an IDN homograph attack. Browsers and email clients often display the IDN version, but the underlying Punycode might reveal a different, suspicious domain. This disparity can easily trick users into believing they are on a legitimate website or receiving an email from a trusted source, when in reality, they are interacting with a fraudulent one. For example, a Cyrillic 'a' can look identical to a Latin 'a', enabling a threat actor to register a domain like apple.com that uses Cyrillic characters, which would then convert to Punycode like xn--pple-4ja.com. This deceptive practice makes it difficult for users to discern legitimate domains from malicious ones, as highlighted by a blog post discussing Punycode attacks from Jamf.
The dark side of IDNs: Homograph attacks
IDN homograph attacks (phishing) pose a serious threat to email security. Attackers register domains that visually mimic legitimate brands, using Punycode to hide their true identity. When an email arrives from such a domain, it often looks authentic, bypassing initial visual checks by unsuspecting recipients. This can lead to credential theft, malware infections, and other forms of cybercrime. The deceptive nature of these domains makes them particularly effective in phishing campaigns. For more information, you can read about IDN homograph attacks on Wikipedia.
Email clients and browsers have implemented various defenses against IDN homograph attacks, such as displaying the Punycode version in the address bar or providing visual warnings. However, these measures are not foolproof. Users must remain vigilant and always double-check the actual domain name, especially when encountering suspicious links or requests for sensitive information. An abnormal characters error could be an indicator of such issues.
Organizations also play a role by monitoring for look-alike domains and implementing robust email authentication protocols such as DMARC, SPF, and DKIM. These protocols help verify the authenticity of email senders and can prevent fraudulent emails from reaching inboxes. Despite advancements, vigilance remains the first line of defense against these sophisticated attacks.
Identifying an IDN phishing attempt
Punycode is a conversion method that represents Unicode characters in domain names using only ASCII characters. This enables domains with non-Latin scripts to function across the internet.
Visual Inspection: Carefully examine the domain name in the address bar or email header. Look for subtle differences or unusual characters.
Punycode Prefix: If you see the xn-- prefix followed by a seemingly random string, it is a Punycode domain. While some legitimate domains use IDNs, be cautious if it's meant to look like a well-known ASCII domain.
Security Warnings: Modern browsers and email clients may display warnings or convert visually similar IDNs to their Punycode form automatically to alert users.
Decoding DNS authorization records
Beyond the subtleties of IDN and Punycode, straightforward misconfigurations of DNS records can also severely impact email deliverability, especially with major providers like Gmail. A common issue arises when Mail Exchanger (MX) records, which direct incoming email to the correct mail server, are incorrectly set up. Instead of pointing to Google's mail servers, they might inadvertently contain values intended for other record types, such as a TXT record used for domain ownership verification.
When a domain's MX record is "screwed up" in this manner, it means that instead of a mail server address (like alt1.aspmx.l.google.com), it might contain a long, seemingly random string that is actually part of a Google site verification TXT record (e.g., google-site-verification=some_long_code). This prevents mail servers from finding the correct destination for emails, causing them to bounce or be discarded. Such an error indicates that the domain cannot receive mail, as there's no valid mail server for inbound delivery.
Example of a screwed up Gmail authorization record
yourdomain.com. IN MX 10 swytcyeidbiwlai5tor3jug7rtovnsgthpxrwgv33is6bfobr2ha.mx-verification.google.com.
Diagnosing this often involves performing a DNS lookup (a 'dig' command) on the domain's MX records. If the output shows a string that resembles a verification token rather than standard Google MX server addresses, you've identified a misconfiguration. This scenario can occur due to manual error when setting up DNS records, often confusing the process of adding a TXT record for verification with the setup of MX records. It highlights the critical importance of verifying all email authentication and DNS records meticulously.
Correct MX record configuration
For Google Workspace (Gmail), MX records should point to specific Google mail servers with assigned priorities. These records ensure that incoming emails are routed correctly to your organization's inboxes.
Purpose: Directs email traffic to the designated mail servers.
Format: Priority number followed by a fully qualified domain name (FQDN) of the mail server.
Example: yourdomain.com. IN MX 1 aspmx.l.google.com.
Screwed up MX record scenario
A common mistake is pasting a TXT record (often a Gmail domain verification string like google-site-verification=...) into the MX record field. This misconfiguration renders email delivery impossible for the domain.
Impact: Emails sent to the domain will fail to deliver, often resulting in bounces or rejections because the sending server cannot resolve a valid mail exchange.
Detection: A dig query for MX records would return a non-mail server address, such as the Google verification string mentioned earlier.
Ensuring ongoing email deliverability and security
Regular monitoring of your DNS records is essential, not just during initial setup but also periodically, to ensure continued email deliverability. Misconfigurations can happen unexpectedly, often after domain transfers, DNS provider changes, or even simple human error. Tools that perform regular DNS health checks can alert you to issues before they severely impact your email communications.
Moreover, robust email authentication practices are paramount. Implementing SPF, DKIM, and DMARC correctly helps legitimate emails pass through spam filters and ensures that recipients trust your messages. These mechanisms also protect your domain from being spoofed by malicious actors, whether they use IDNs or standard ASCII domains. Neglecting these can lead to your emails consistently landing in spam folders or being rejected outright, impacting your domain reputation.
Finally, user education plays a vital role. Training employees and customers to recognize the signs of phishing, including suspicious domain names (both IDN and regular), is crucial. Encourage them to verify sender authenticity and to be wary of unexpected emails requesting sensitive information. A multi-layered approach combining technical safeguards with user awareness is the most effective defense against email-borne threats.
Views from the trenches
Best practices
Actively monitor your DNS records, including MX and TXT records, for any changes or errors, especially after domain transfers or configuration updates.
Implement a strict DMARC policy (p=quarantine or p=reject) to prevent email spoofing and ensure only authorized senders use your domain.
Educate your users and employees about IDN homograph attacks and other phishing techniques, emphasizing vigilance and how to spot suspicious domains.
Regularly review your email authentication reports to detect and troubleshoot any SPF, DKIM, or DMARC failures, which can indicate misconfigurations or malicious activity.
Common pitfalls
Mistaking a TXT record for an MX record when configuring DNS for email services like Google Workspace, leading to mail delivery failures.
Failing to monitor your domain for IDN homograph registrations that mimic your brand, which can be used in phishing attacks against your customers.
Assuming that once DNS records are set, they will remain correct indefinitely, without accounting for potential changes or accidental deletions.
Not having a robust DMARC policy, leaving your domain vulnerable to impersonation and your legitimate emails susceptible to spam folders.
Expert tips
Leverage DMARC aggregate reports to gain visibility into email authentication results, which can help detect misconfigured DNS records or phishing attempts leveraging your domain.
Utilize online tools to convert suspicious IDN domains to their Punycode representation to reveal their true underlying ASCII form for better identification.
Set up alerts for changes to critical DNS records to be immediately notified of any unauthorized modifications that could affect email flow or security.
Consider blocking email addresses from domains with Punycode in your email system unless they are explicitly whitelisted and known to be legitimate.
Marketer view
Marketer from Email Geeks says they were confused about an xn-- prefixed domain in an email, and online tools indicated it was fine, but suspected it shouldn't be used.
2020-11-12 - Email Geeks
Expert view
Expert from Email Geeks says that the domain is likely an IDN (Internationalized Domain Name) or Punycode, meaning it appears differently in its original language, and sending to it should be avoided.
2020-11-12 - Email Geeks
Navigating domain complexities for secure email
The world of domain names, particularly with the introduction of Internationalized Domain Names and their Punycode representations, presents both opportunities for global reach and significant security challenges. While IDNs facilitate broader internet accessibility, their potential for misuse in homograph attacks necessitates constant vigilance from both email users and administrators.
Equally critical is the accurate configuration of DNS records, especially for email authorization. A simple misplacement of a verification string into an MX record can cripple email deliverability, preventing legitimate communications from reaching their intended recipients. By understanding these technical nuances, regularly auditing DNS settings, and implementing robust authentication protocols, organizations can significantly bolster their email security posture and ensure reliable message delivery in today's complex digital landscape.
Gmail. A common issue arises when Mail Exchanger (MX) records, which direct incoming email to the correct mail server, are incorrectly set up. Instead of pointing to 
Google's mail servers, they might inadvertently contain values intended for other record types, such as a TXT record used for domain ownership verification.
