What is the maximum number of characters allowed in a DMARC TXT record?
Michael Ko
Co-founder & CEO, Suped
Published 18 Nov 2024
Updated 2 Oct 2025
10 min read
When you set up to secure your email domain, you'll need to publish a DMARC record in your DNS. This record is a type of TXT record, and like all DNS records, it comes with certain length limitations that are important to understand. Failing to adhere to these limits can lead to DMARC misconfigurations, authentication failures, and ultimately, email deliverability issues.
The primary rule to remember is that a single string within a DNS TXT record is limited to 255 characters. This is a fundamental constraint of the DNS protocol. However, DMARC records can sometimes become quite lengthy, especially with multiple reporting addresses or complex policies. This often raises the question of how to publish a DMARC record that exceeds this 255-character limit.
Fortunately, DNS allows for TXT records to contain multiple strings. When you publish a record with several quoted strings, DNS resolvers (like those used by email providers) automatically concatenate these strings into one continuous value. This means that while no single quoted section can exceed 255 characters, the overall DMARC record can be much longer, provided it is split correctly. Let's delve into the specifics of these limits and how to manage them.
The technicalities of DNS TXT record length
While the 255-character limit applies to each individual string within a TXT record, the actual maximum length for an entire TXT record, after concatenation, varies by DNS provider. Many providers support a total length of up to 2048 characters, and some even extend this to 4000 characters. For example, DigiCert notes the 255 character limit for a single string, and services like AWS Route 53 allow for up to 4,000 characters when multiple strings are used. It's always best to check with your specific DNS host for their exact maximums.
When a DMARC record needs to be longer than a single 255-character string, you split the value into multiple quoted segments. The key is that these segments must appear consecutively within the same TXT record entry in your DNS settings. The DNS server will then combine them into a single logical record for email recipients to process. This mechanism is crucial for accommodating comprehensive DMARC policies without hitting hard limits on individual strings.
However, just splitting the record isn't enough; it must be done correctly. Each segment needs to be a valid, quoted string. Incorrect splitting can lead to parsing errors, rendering your DMARC record ineffective. This is particularly important for services that parse these records to determine email authenticity, such as Gmail and Yahoo's new sender requirements, which place a high emphasis on properly configured authentication.
DNS record splitting explained
When a TXT record value exceeds 255 characters, it must be divided into multiple quoted strings. DNS servers will then concatenate these strings into a single, cohesive record when queried. For example, if your DMARC record is very long, it would look something like this:
Note the quotation marks around each segment. This instructs DNS to treat them as distinct, yet linked, parts of the same overall record.
DMARC record specific considerations
DMARC records are essentially sophisticated text strings that communicate your email authentication policy to receiving mail servers. These records use various tags and values to define actions like policy (p), reporting addresses (rua, ruf), and alignment modes (aspf, adkim). While some tags like pct have minimal impact on length, the rua (aggregate report URI) and ruf (forensic report URI) tags can significantly contribute to the overall record length. This is because you might specify multiple email addresses or webhooks to receive reports, each adding to the character count.
Consider a DMARC record that includes several rua addresses for different DMARC reporting services. Each mailto: URI and the email address itself contributes characters. If you exceed the 255-character threshold for a single string, your DNS provider will expect you to split the record into multiple quoted parts. This splitting must occur at a logical break point, typically between tags or after a comma-separated value within a tag, to ensure the record remains parsable.
Incorrectly breaking a DMARC record, such as splitting a tag or an email address in the middle, can lead to your DMARC policy being misinterpreted or ignored entirely. This is similar to how SPF records need careful formatting to avoid issues. Always ensure that each quoted string forms a complete and syntactically correct portion of the DMARC record when split.
Poorly formatted DMARC record
A single, unbroken string exceeding 255 characters, or a string broken mid-tag:
The consequences of an improperly configured or overly long DMARC record can be severe for your email program. If mail servers cannot parse your DMARC record, it's as if you don't have one at all. This leaves your domain vulnerable to phishing and spoofing attacks, eroding trust in your brand and potentially landing your legitimate emails in spam folders or having them blocked outright. Managing DNS TXT record length limits is a critical part of maintaining email security and deliverability.
Receiving mail servers rely on accurately parsed DMARC records to determine if an incoming email is legitimate. If your record is too long or malformed due to incorrect splitting, they may default to a less strict policy, or even reject your email, impacting your domain reputation. Moreover, a DMARC record that is not properly configured can hide genuine authentication issues, making it harder to diagnose underlying deliverability problems.
Another often overlooked aspect is that some DNS providers may have specific quirks or lower maximum limits than the industry standard. This means a record that works perfectly with one provider might fail with another. Always verify your DMARC record's integrity and monitor its performance across various email ecosystems to ensure consistent enforcement of your email policy. Being proactive in this area helps safeguard your email communications.
Authentication failures: Emails may fail DMARC checks, even if they are legitimate, leading to rejection or placement in spam folders.
Increased spoofing risk: Without a parsable DMARC record, your domain is more susceptible to impersonation and malicious attacks, as receiving servers cannot enforce your policy.
Poor deliverability: Legitimate emails might be marked as spam or blocked, impacting your communication effectiveness and business operations.
Consequences of an invalid DMARC record
An invalid DMARC record can lead to severe issues. If a DMARC record is too long or improperly split, it can be misread or ignored by receiving mail servers. This compromises your email security, opens the door to phishing attacks, and can seriously harm your email deliverability rates, causing your important messages to go to spam or be rejected.
Best practices for DMARC record management
To ensure your DMARC records are always correctly configured and within the permissible length limits, follow these best practices. Start by crafting a concise DMARC record, avoiding unnecessary tags or excessively long report URIs where possible. When multiple rua or ruf addresses are needed, make sure to split your record into properly quoted 255-character segments. Use a DMARC record generator to help you construct your record correctly from the outset.
Regularly check your published DMARC record using a DNS lookup tool to confirm it resolves as expected and that all segments are concatenated properly. Any error in publishing, even a missing quote mark, can lead to your DMARC policy being ineffective. This proactive verification can save you from deliverability headaches down the line and ensure your email security remains robust.
Remember that DMARC is part of a larger email authentication ecosystem that includes SPF and DKIM. Sometimes, issues with SPF records, such as exceeding the 10-DNS-lookup limit, can indirectly impact DMARC by causing authentication failures. Tools that offer SPF flattening can help simplify your SPF record and reduce its overall length, contributing to better DNS hygiene. This holistic approach to email authentication strengthens your overall domain security.
Tag
Description
Length Impact
v
Protocol version
Minimal (always DMARC1)
p
Policy for domain
Minimal (e.g., none, quarantine, reject)
rua
Aggregate report URI
High, especially with multiple comma-separated URIs
ruf
Forensic report URI
High, similar to rua, with multiple URIs
Using a robust DMARC monitoring tool like Suped can significantly simplify the process of managing DMARC records and ensuring compliance. Our platform offers AI-powered recommendations that guide you in fixing issues, including those related to record length, and strengthening your policy. With real-time alerts, you'll be notified immediately if any DMARC issues arise, including parsing errors due to length. Our unified platform monitors DMARC, SPF, and DKIM, providing a comprehensive view of your email security and deliverability.
For MSPs and agencies, our multi-tenancy dashboard makes managing multiple domains easy and efficient. Our free plan also allows you to get started without any commitment, offering a generous set of features to begin monitoring your DMARC records and ensuring optimal email delivery.
Ensuring optimal DMARC deployment
Understanding and adhering to the maximum character limits for DMARC TXT records is not just a technicality; it's a critical component of effective email authentication and deliverability. While a single string is limited to 255 characters, the ability to split records into multiple quoted segments allows for more complex policies, provided they are implemented correctly.
The overall limit for a DMARC TXT record varies by DNS provider, typically ranging from 2048 to 4000 characters. Always consult your provider's documentation and carefully construct your records. Misconfiguration due to length or incorrect splitting can lead to DMARC authentication failures, increased risk of domain spoofing, and negatively impact your email deliverability. Proactive monitoring and validation are essential steps.
Leveraging specialized tools like Suped provides the visibility and actionable insights needed to confidently deploy and maintain robust DMARC protection, ensuring your emails reach their intended recipients securely.
