These tools help visualize the data, identify trends, and pinpoint any issues with your email authentication setup. They can highlight sources of unauthorized email, identify misconfigured SPF or DKIM records, and provide actionable insights to improve your email deliverability and security.

By implementing DMARC, you can gain greater control over your email ecosystem, protect your brand from spoofing attacks, and improve your email deliverability rates.

Testing and Monitoring Your Email Authentication

Implementing SPF, DKIM, and DMARC is just the first step. It’s crucial to continuously test and monitor your email authentication configuration to ensure it’s working correctly and to identify any potential issues that may arise.

Regular testing helps you proactively identify misconfigurations or changes that could impact your email deliverability. Monitoring allows you to track your email authentication results over time, detect potential spoofing attempts, and fine-tune your policies.

Testing Your SPF and DKIM Configuration

There are several ways to test your SPF and DKIM configuration:

• Using Online Email Authentication Checkers: Several online tools can check your SPF and DKIM configuration by sending an email to a designated address and analyzing the email headers.
• Manually Analyzing Email Headers: You can manually analyze the email headers of emails sent from your domain to check for SPF and DKIM pass/fail results.
• Using Command-Line Tools: You can use command-line tools like dig and nslookup to query your DNS records and verify that your SPF and DKIM records are configured correctly.

Example 1: Using an online email authentication checker (Mail-Tester.com)

1. Go to Mail-Tester.com.
2. Copy the unique email address provided on the website.
3. Send an email from your domain to the provided email address.
4. Click the “Then check your score” button on Mail-Tester.com.
5. Mail-Tester.com will analyze your email and provide a score and detailed report of your email authentication results, including SPF, DKIM, and DMARC.

DMARC reports can be initially challenging to parse due to their XML format. Many online tools can help convert these XML reports into more readable formats and provide insightful analysis. Examples include:

• dmarcian’s DMARC Report Analyzer
• EasyDMARC’s DMARC Report Analyzer
• Agari Brand Protection

These tools help visualize the data, identify trends, and pinpoint any issues with your email authentication setup. They can highlight sources of unauthorized email, identify misconfigured SPF or DKIM records, and provide actionable insights to improve your email deliverability and security.

By implementing DMARC, you can gain greater control over your email ecosystem, protect your brand from spoofing attacks, and improve your email deliverability rates.

Testing and Monitoring Your Email Authentication

Implementing SPF, DKIM, and DMARC is just the first step. It’s crucial to continuously test and monitor your email authentication configuration to ensure it’s working correctly and to identify any potential issues that may arise.

Regular testing helps you proactively identify misconfigurations or changes that could impact your email deliverability. Monitoring allows you to track your email authentication results over time, detect potential spoofing attempts, and fine-tune your policies.

Testing Your SPF and DKIM Configuration

There are several ways to test your SPF and DKIM configuration:

• Using Online Email Authentication Checkers: Several online tools can check your SPF and DKIM configuration by sending an email to a designated address and analyzing the email headers.
• Manually Analyzing Email Headers: You can manually analyze the email headers of emails sent from your domain to check for SPF and DKIM pass/fail results.
• Using Command-Line Tools: You can use command-line tools like dig and nslookup to query your DNS records and verify that your SPF and DKIM records are configured correctly.

Example 1: Using an online email authentication checker (Mail-Tester.com)

1. Go to Mail-Tester.com.
2. Copy the unique email address provided on the website.
3. Send an email from your domain to the provided email address.
4. Click the “Then check your score” button on Mail-Tester.com.
5. Mail-Tester.com will analyze your email and provide a score and detailed report of your email authentication results, including SPF, DKIM, and DMARC.

This record sets a strict reject policy for both the main domain and all subdomains (`p=reject; sp=reject`). It also enforces strict alignment for both DKIM and SPF (`adkim=s; aspf=s`). Aggregate reports are sent to `dmarc-aggregate@example.com`, and forensic reports are sent to `dmarc-forensic@example.com`. Forensic reports are triggered by any authentication failure (`fo=1`). This is a strong DMARC configuration suitable for organizations with mature email authentication practices.

Understanding DMARC Alignment

DMARC alignment refers to the relationship between the domain used in the “From” header of the email and the domains used in the SPF and DKIM authentication checks. DMARC requires either SPF or DKIM to “align” with the “From” domain for the email to pass DMARC authentication.

There are two types of alignment: strict and relaxed.

• Strict Alignment: For DKIM, the “d=” tag in the DKIM signature must exactly match the domain in the “From” header. For SPF, the domain used to perform the SPF check must exactly match the domain in the “From” header.
• Relaxed Alignment: For DKIM, the “d=” tag in the DKIM signature must be a subdomain of the domain in the “From” header. For SPF, the domain used to perform the SPF check must be the same as or a subdomain of the domain in the “From” header.

The alignment mode is specified using the adkim and aspf tags in the DMARC record. The default alignment mode is relaxed.

Strict alignment provides stronger protection against spoofing, but it can also be more difficult to configure correctly. Relaxed alignment is more forgiving but provides less protection against spoofing.

Analyzing DMARC Reports

DMARC reports provide valuable insights into your email authentication ecosystem. There are two types of DMARC reports:

• Aggregate Reports: These reports provide a summary of email authentication results, including the number of emails that passed and failed SPF and DKIM, the DMARC policy applied, and the source IP addresses of the emails. Aggregate reports are typically sent daily or weekly and are in XML format.
• Forensic Reports: These reports provide detailed information about individual email authentication failures, including the full email headers and body. Forensic reports are typically sent in real-time and can contain personally identifiable information (PII). Use with caution and ensure compliance with privacy regulations.

Analyzing DMARC reports can help you identify and troubleshoot email authentication issues, detect potential spoofing attacks, and fine-tune your DMARC policy.

There are various tools available to help you analyze DMARC reports, including online DMARC report analyzers and commercial DMARC monitoring services.

DMARC reports can be initially challenging to parse due to their XML format. Many online tools can help convert these XML reports into more readable formats and provide insightful analysis. Examples include:

• dmarcian’s DMARC Report Analyzer
• EasyDMARC’s DMARC Report Analyzer
• Agari Brand Protection

These tools help visualize the data, identify trends, and pinpoint any issues with your email authentication setup. They can highlight sources of unauthorized email, identify misconfigured SPF or DKIM records, and provide actionable insights to improve your email deliverability and security.

By implementing DMARC, you can gain greater control over your email ecosystem, protect your brand from spoofing attacks, and improve your email deliverability rates.

Testing and Monitoring Your Email Authentication

Implementing SPF, DKIM, and DMARC is just the first step. It’s crucial to continuously test and monitor your email authentication configuration to ensure it’s working correctly and to identify any potential issues that may arise.

Regular testing helps you proactively identify misconfigurations or changes that could impact your email deliverability. Monitoring allows you to track your email authentication results over time, detect potential spoofing attempts, and fine-tune your policies.

Testing Your SPF and DKIM Configuration

There are several ways to test your SPF and DKIM configuration:

• Using Online Email Authentication Checkers: Several online tools can check your SPF and DKIM configuration by sending an email to a designated address and analyzing the email headers.
• Manually Analyzing Email Headers: You can manually analyze the email headers of emails sent from your domain to check for SPF and DKIM pass/fail results.
• Using Command-Line Tools: You can use command-line tools like dig and nslookup to query your DNS records and verify that your SPF and DKIM records are configured correctly.

Example 1: Using an online email authentication checker (Mail-Tester.com)

1. Go to Mail-Tester.com.
2. Copy the unique email address provided on the website.
3. Send an email from your domain to the provided email address.
4. Click the “Then check your score” button on Mail-Tester.com.
5. Mail-Tester.com will analyze your email and provide a score and detailed report of your email authentication results, including SPF, DKIM, and DMARC.

Example 4: A more comprehensive DMARC record:

_dmarc.example.com. IN TXT "v=DMARC1; p=reject; sp=reject; adkim=s; aspf=s; ruf=mailto:dmarc-aggregate@example.com; rf=mailto:dmarc-forensic@example.com; fo=1"

This record sets a strict reject policy for both the main domain and all subdomains (`p=reject; sp=reject`). It also enforces strict alignment for both DKIM and SPF (`adkim=s; aspf=s`). Aggregate reports are sent to `dmarc-aggregate@example.com`, and forensic reports are sent to `dmarc-forensic@example.com`. Forensic reports are triggered by any authentication failure (`fo=1`). This is a strong DMARC configuration suitable for organizations with mature email authentication practices.

Understanding DMARC Alignment

DMARC alignment refers to the relationship between the domain used in the “From” header of the email and the domains used in the SPF and DKIM authentication checks. DMARC requires either SPF or DKIM to “align” with the “From” domain for the email to pass DMARC authentication.

There are two types of alignment: strict and relaxed.

• Strict Alignment: For DKIM, the “d=” tag in the DKIM signature must exactly match the domain in the “From” header. For SPF, the domain used to perform the SPF check must exactly match the domain in the “From” header.
• Relaxed Alignment: For DKIM, the “d=” tag in the DKIM signature must be a subdomain of the domain in the “From” header. For SPF, the domain used to perform the SPF check must be the same as or a subdomain of the domain in the “From” header.

The alignment mode is specified using the adkim and aspf tags in the DMARC record. The default alignment mode is relaxed.

Strict alignment provides stronger protection against spoofing, but it can also be more difficult to configure correctly. Relaxed alignment is more forgiving but provides less protection against spoofing.

Analyzing DMARC Reports

DMARC reports provide valuable insights into your email authentication ecosystem. There are two types of DMARC reports:

• Aggregate Reports: These reports provide a summary of email authentication results, including the number of emails that passed and failed SPF and DKIM, the DMARC policy applied, and the source IP addresses of the emails. Aggregate reports are typically sent daily or weekly and are in XML format.
• Forensic Reports: These reports provide detailed information about individual email authentication failures, including the full email headers and body. Forensic reports are typically sent in real-time and can contain personally identifiable information (PII). Use with caution and ensure compliance with privacy regulations.

Analyzing DMARC reports can help you identify and troubleshoot email authentication issues, detect potential spoofing attacks, and fine-tune your DMARC policy.

There are various tools available to help you analyze DMARC reports, including online DMARC report analyzers and commercial DMARC monitoring services.

DMARC reports can be initially challenging to parse due to their XML format. Many online tools can help convert these XML reports into more readable formats and provide insightful analysis. Examples include:

• dmarcian’s DMARC Report Analyzer
• EasyDMARC’s DMARC Report Analyzer
• Agari Brand Protection

These tools help visualize the data, identify trends, and pinpoint any issues with your email authentication setup. They can highlight sources of unauthorized email, identify misconfigured SPF or DKIM records, and provide actionable insights to improve your email deliverability and security.

By implementing DMARC, you can gain greater control over your email ecosystem, protect your brand from spoofing attacks, and improve your email deliverability rates.

Testing and Monitoring Your Email Authentication

Implementing SPF, DKIM, and DMARC is just the first step. It’s crucial to continuously test and monitor your email authentication configuration to ensure it’s working correctly and to identify any potential issues that may arise.

Regular testing helps you proactively identify misconfigurations or changes that could impact your email deliverability. Monitoring allows you to track your email authentication results over time, detect potential spoofing attempts, and fine-tune your policies.

Testing Your SPF and DKIM Configuration

There are several ways to test your SPF and DKIM configuration:

• Using Online Email Authentication Checkers: Several online tools can check your SPF and DKIM configuration by sending an email to a designated address and analyzing the email headers.
• Manually Analyzing Email Headers: You can manually analyze the email headers of emails sent from your domain to check for SPF and DKIM pass/fail results.
• Using Command-Line Tools: You can use command-line tools like dig and nslookup to query your DNS records and verify that your SPF and DKIM records are configured correctly.

Example 1: Using an online email authentication checker (Mail-Tester.com)

1. Go to Mail-Tester.com.
2. Copy the unique email address provided on the website.
3. Send an email from your domain to the provided email address.
4. Click the “Then check your score” button on Mail-Tester.com.
5. Mail-Tester.com will analyze your email and provide a score and detailed report of your email authentication results, including SPF, DKIM, and DMARC.

Email Marketing Secrets: Mastering Authentication to Bypass Spam Filters

Email marketing remains a powerful tool, but its effectiveness hinges on reaching the inbox, not the spam folder. Implementing robust email authentication protocols is paramount to proving your legitimacy and avoiding those dreaded spam filters. This article dives deep into the essential authentication methods – SPF, DKIM, and DMARC – providing practical examples and configurations to ensure your emails land where they belong.

We’ll move beyond the theoretical and provide concrete steps, including DNS record configuration, testing procedures, and troubleshooting tips, all designed to elevate your email deliverability rates. Get ready to take control of your email reputation and connect with your audience effectively.

Table of Contents

• Understanding SPF: Defining Authorized Sending Servers
• Implementing DKIM: Digitally Signing Your Emails
• Setting Up DMARC: Policy Enforcement and Reporting
• Testing and Monitoring Your Email Authentication

Understanding SPF: Defining Authorized Sending Servers

Sender Policy Framework (SPF) is an email authentication method designed to prevent spammers from using your domain to send unauthorized emails. It works by specifying which mail servers are authorized to send emails on behalf of your domain. Recipient mail servers check the SPF record of the sender’s domain to verify if the sending server is listed as authorized. If the server isn’t listed, the email is more likely to be marked as spam.

The SPF record is a TXT record added to your domain’s DNS settings. It contains a version number, mechanisms to specify authorized servers, and qualifiers to determine how recipient servers should handle emails that fail the SPF check. A well-configured SPF record significantly improves your email deliverability.

Crafting Your SPF Record

An SPF record consists of tags that define which servers are allowed to send emails on behalf of your domain. Here’s a breakdown of the most common tags:

• v=spf1: Specifies the SPF version (currently spf1).
• ip4:: Allows specific IPv4 addresses to send emails.
• ip6:: Allows specific IPv6 addresses to send emails.
• a: Allows the IP address of the domain’s A record to send emails.
• mx: Allows the IP addresses of the domain’s MX records to send emails.
• include:: Includes the SPF record of another domain. This is useful if you use third-party email services.
• -all: Denies all other servers not explicitly listed. This is the recommended ending for your SPF record.
• ~all: Softfail for all other servers not explicitly listed. This means the email will be accepted but marked as potentially spam.
• +all: Allows all servers to send emails. This is highly discouraged as it renders SPF ineffective.

Example 1: Basic SPF Record

v=spf1 ip4:192.0.2.0/24 -all

This SPF record authorizes all IPv4 addresses in the 192.0.2.0/24 range to send emails on behalf of your domain. All other servers are explicitly denied.

Example 2: SPF Record with Multiple Sources and an Include Statement

v=spf1 ip4:192.0.2.0/24 ip6:2001:db8::/32 include:servers.example.com -all

This SPF record authorizes IPv4 addresses in the 192.0.2.0/24 range, IPv6 addresses in the 2001:db8::/32 range, and any servers authorized by the SPF record of servers.example.com. All other servers are denied.

Example 3: SPF Record for Google Workspace (formerly G Suite)

v=spf1 include:_spf.google.com -all

If you use Google Workspace for email, this is the recommended SPF record. It includes Google’s SPF record, which authorizes Google’s servers to send emails on your behalf. No other servers are authorized.

Adding the SPF Record to Your DNS

Once you’ve crafted your SPF record, you need to add it to your domain’s DNS settings. The exact steps vary depending on your DNS provider (e.g., GoDaddy, Cloudflare, Namecheap). However, the general process is the same:

• Log in to your DNS provider’s control panel.
• Find the DNS settings for your domain.
• Add a new TXT record.
• In the “Name” or “Host” field, enter “@” or leave it blank (depending on your provider).
• In the “Value” or “Text” field, paste your SPF record.
• Save the changes.

Example: Adding an SPF record in Cloudflare

1. Log in to your Cloudflare account.
2. Select your domain.
3. Go to the “DNS” tab.
4. Click “Add record”.
5. Select “TXT” as the type.
6. In the “Name” field, enter “@”.
7. In the “Content” field, paste your SPF record: v=spf1 include:_spf.google.com -all
8. Click “Save”.

Important Note: You can only have one SPF record for a domain. If you have multiple email sending services, you must combine them into a single SPF record using the include: mechanism.

Common SPF Mistakes to Avoid

• Having multiple SPF records: This will cause SPF to fail.
• Using +all: This effectively disables SPF and makes your domain vulnerable to spoofing.
• Not including all authorized sending servers: Emails from servers not listed in your SPF record will likely be marked as spam.
• Exceeding the SPF record lookup limit: SPF has a limit of 10 DNS lookups. Using too many include: statements can exceed this limit. If you reach the lookup limit, consider using a service that flattens your SPF record.
• Not updating your SPF record when you change email providers: Failing to update your SPF record can lead to deliverability issues.

An example of exceeding the lookup limit:

v=spf1 include:spf1.example.com include:spf2.example.com include:spf3.example.com include:spf4.example.com include:spf5.example.com include:spf6.example.com include:spf7.example.com include:spf8.example.com include:spf9.example.com include:spf10.example.com -all

Even if each of those `include:` statements had a single lookup, this would exceed the limit, causing SPF to fail. Consider using tools to flatten these SPF records or re-evaluate your email sending practices.

By understanding and correctly implementing SPF, you can significantly improve your email deliverability and protect your domain from spoofing.

Implementing DKIM: Digitally Signing Your Emails

DomainKeys Identified Mail (DKIM) provides a method to associate a domain name with an email message, thereby allowing a receiving system to verify that a message was sent by an authorized sender. DKIM uses cryptographic authentication to prove that the email hasn’t been tampered with during transit and that it truly originated from the claimed domain. This adds another layer of trust and significantly boosts email deliverability.

Unlike SPF, which focuses on authorized sending servers, DKIM focuses on the content of the email itself. It does this by adding a digital signature to the email header using a private key. The recipient’s mail server then retrieves the corresponding public key from the sender’s DNS record and uses it to verify the signature. If the signature is valid, the recipient server can be confident that the email hasn’t been altered and that it genuinely came from the claimed sender.

Generating a DKIM Key Pair

The first step in implementing DKIM is to generate a cryptographic key pair: a private key and a public key. The private key is used to sign the outgoing emails, and the public key is published in your DNS record. It’s crucial to keep the private key secure.

You can generate a DKIM key pair using various tools, including OpenSSL or your email service provider’s interface. Here’s an example using OpenSSL:

openssl genrsa -out private.key 2048
openssl rsa -in private.key -pubout -out public.key

These commands will generate two files: private.key (containing the private key) and public.key (containing the public key). Keep the private key safe!

For security reasons, it’s recommended to use a key length of at least 2048 bits. Using shorter key lengths may make your DKIM signature vulnerable to attacks.

Alternatively, many ESPs (Email Service Providers) such as SendGrid, Mailgun, and Amazon SES will automatically generate the DKIM key pair for you within their platform. Using your ESP’s provided tools is often easier and less prone to error.

Adding the DKIM Public Key to Your DNS

Once you have the public key, you need to add it to your domain’s DNS settings as a TXT record. The exact steps are similar to adding an SPF record. However, the format of the DKIM record is slightly different.

The DKIM record consists of a selector, which is a unique identifier for the DKIM key. The selector is used by the recipient server to locate the correct public key in your DNS. Common selectors include “default” or “mail”.

The general format of the DKIM record is:

selector._domainkey.yourdomain.com.  IN TXT  "v=DKIM1; k=rsa; p=PUBLIC_KEY;"

Where:

• selector: The DKIM selector (e.g., “default”).
• yourdomain.com: Your domain name.
• v=DKIM1: Specifies the DKIM version (currently DKIM1).
• k=rsa: Specifies the key type (RSA).
• p=PUBLIC_KEY: Your public key (without the “—–BEGIN PUBLIC KEY—–” and “—–END PUBLIC KEY—–” lines, and with all line breaks removed).

Example: Adding a DKIM record with selector “mail”

Let’s say your domain is example.com, and your public key is:

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAw9eKxLNPjX3C2H6b7
... (rest of the key) ...
zWgIDAQAB
-----END PUBLIC KEY-----

Then your DKIM record would look like this:

mail._domainkey.example.com.  IN TXT  "v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAw9eKxLNPjX3C2H6b7...zWgIDAQAB;"

Remember to remove the “—–BEGIN PUBLIC KEY—–” and “—–END PUBLIC KEY—–” lines and remove any line breaks within the public key itself. Many DNS providers have character limits for TXT records. If your public key is too long, you may need to split it into multiple strings within the same record, like this:

mail._domainkey.example.com. IN TXT "v=DKIM1; k=rsa; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAw9eKxLNPjX3C2H6b7" "..." "zWgIDAQAB;"

Consult your DNS provider’s documentation for specific instructions on handling long TXT records.

Configuring Your Email Server to Sign Outgoing Emails

Once you’ve added the DKIM record to your DNS, you need to configure your email server to sign outgoing emails using the private key. The exact steps vary depending on your email server software. Here are some examples:

• Postfix: You can use the opendkim or dkim-milter packages to sign outgoing emails.
• Sendmail: You can use the dkim-milter package to sign outgoing emails.
• Exim: Exim has built-in DKIM support. You’ll need to configure the DKIM settings in your Exim configuration file.

Example: Configuring Postfix with OpenDKIM on Debian/Ubuntu

1. Install the opendkim and opendkim-tools packages:

   sudo apt-get update
   sudo apt-get install opendkim opendkim-tools

2. Generate a key table:

   sudo opendkim-genkey -d example.com -s mail -v

   This will create two files: mail.private and mail.txt. The `mail.txt` file contains the DNS record you need to add.
3. Move the private key to the OpenDKIM key table directory:

   sudo mv mail.private /etc/opendkim/keys/

4. Set the correct ownership and permissions for the private key:

   sudo chown opendkim:opendkim /etc/opendkim/keys/mail.private
   sudo chmod 600 /etc/opendkim/keys/mail.private

5. Edit the OpenDKIM configuration file (/etc/opendkim.conf) and add the following lines:

   Domain                  example.com
   KeyFile                 /etc/opendkim/keys/mail.private
   Selector                mail
   Socket                  inet:12301@localhost
   UserID                  opendkim:opendkim
   

6. Edit the OpenDKIM trusted hosts file (/etc/opendkim/TrustedHosts) and add your server’s IP address and domain name.
7. Edit the Postfix configuration file (/etc/postfix/main.cf) and add the following lines:

   milter_default_action = accept
   milter_protocol = 2
   smtpd_milters = inet:127.0.0.1:12301
   non_smtpd_milters = inet:127.0.0.1:12301

8. Restart OpenDKIM and Postfix:

   sudo systemctl restart opendkim
   sudo systemctl restart postfix

This configuration tells Postfix to use OpenDKIM to sign outgoing emails from the example.com domain using the private key stored in /etc/opendkim/keys/mail.private.

Consult your email server software’s documentation for detailed instructions on configuring DKIM signing.

DKIM Best Practices

• Use a strong key length (2048 bits or higher).
• Keep your private key secure.
• Rotate your DKIM keys periodically. This helps to mitigate the risk of key compromise.
• Monitor your DKIM signing process. Check your email logs for errors related to DKIM signing.
• Use a unique selector for each DKIM key. This makes it easier to rotate keys without disrupting email delivery.

By properly implementing DKIM, you can significantly increase the trustworthiness of your emails and improve your deliverability rates. It’s a crucial step in protecting your brand reputation and ensuring that your messages reach your intended recipients.

Setting Up DMARC: Policy Enforcement and Reporting

Domain-based Message Authentication, Reporting & Conformance (DMARC) builds upon SPF and DKIM to provide a comprehensive email authentication framework. DMARC allows domain owners to specify how recipient mail servers should handle emails that fail SPF and DKIM checks. Furthermore, it provides a mechanism for receiving reports about email authentication results, allowing you to monitor your email ecosystem and identify potential abuse.

Think of DMARC as the policy enforcer. SPF and DKIM are the verification methods, and DMARC tells receiving servers *what to do* with emails that fail those checks. Without DMARC, receiving servers are left to their own devices, potentially delivering unauthenticated emails to the inbox, marking them as spam, or silently discarding them. DMARC allows you to explicitly state your preferences, significantly reducing the chances of spoofed emails reaching your recipients and damaging your brand reputation.

Understanding DMARC Policies

DMARC defines three primary policies that you can specify in your DMARC record:

• none: This policy instructs recipient servers to take no specific action on emails that fail SPF and DKIM checks. This is typically used for monitoring and gathering data.
• quarantine: This policy instructs recipient servers to place emails that fail SPF and DKIM checks into the recipient’s spam folder.
• reject: This policy instructs recipient servers to reject emails that fail SPF and DKIM checks. This is the most strict policy and provides the strongest protection against spoofing.

It’s recommended to start with the none policy to monitor your email authentication results and identify any legitimate emails that might be failing SPF or DKIM. Once you’re confident that your email authentication is properly configured, you can gradually move to the quarantine and eventually the reject policy.

Creating Your DMARC Record

The DMARC record is a TXT record added to your domain’s DNS settings. It’s located at _dmarc.yourdomain.com.

The DMARC record contains several tags that define your DMARC policy and reporting preferences. Here’s a breakdown of the most common tags:

• v=DMARC1: Specifies the DMARC version (currently DMARC1).
• p=: Specifies the DMARC policy (none, quarantine, or reject).
• sp=: Specifies the policy for subdomains. If not specified, it defaults to the policy specified by `p`.
• adkim=: Specifies the DKIM alignment mode (r for relaxed, s for strict).
• aspf=: Specifies the SPF alignment mode (r for relaxed, s for strict).
• ruf=mailto:: Specifies the email address to which aggregate reports should be sent. These reports provide a summary of email authentication results.
• ruf=mailto:: Specifies the email address to which forensic reports (also known as failure reports) should be sent. These reports provide detailed information about individual email authentication failures. Use with caution, as these reports can contain personally identifiable information (PII).
• fo=: Specifies the reporting options for forensic reports.
• pct=: Specifies the percentage of messages to which the DMARC policy should be applied. This allows you to gradually roll out your DMARC policy. It is deprecated.

Example 1: DMARC record for monitoring only

_dmarc.example.com.  IN TXT  "v=DMARC1; p=none; ruf=mailto:dmarc-reports@example.com;"

This DMARC record specifies a policy of none, meaning that recipient servers should take no specific action on emails that fail SPF and DKIM checks. It also specifies that aggregate reports should be sent to dmarc-reports@example.com. This is a good starting point for monitoring your email authentication results.

Example 2: DMARC record for quarantining failing emails

_dmarc.example.com.  IN TXT  "v=DMARC1; p=quarantine; ruf=mailto:dmarc-reports@example.com;"

This DMARC record specifies a policy of quarantine, meaning that recipient servers should place emails that fail SPF and DKIM checks into the recipient’s spam folder. It also specifies that aggregate reports should be sent to dmarc-reports@example.com. This is a good next step after monitoring.

Example 3: DMARC record for rejecting failing emails and requesting forensic reports

_dmarc.example.com.  IN TXT  "v=DMARC1; p=reject; ruf=mailto:dmarc-reports@example.com; rf=mailto:forensic-reports@example.com; fo=1;"

This DMARC record specifies a policy of reject, meaning that recipient servers should reject emails that fail SPF and DKIM checks. It also specifies that aggregate reports should be sent to dmarc-reports@example.com and forensic reports should be sent to forensic-reports@example.com. The fo=1 tag specifies that forensic reports should be generated if either SPF or DKIM fails.

Example 4: A more comprehensive DMARC record:

_dmarc.example.com. IN TXT "v=DMARC1; p=reject; sp=reject; adkim=s; aspf=s; ruf=mailto:dmarc-aggregate@example.com; rf=mailto:dmarc-forensic@example.com; fo=1"

This record sets a strict reject policy for both the main domain and all subdomains (`p=reject; sp=reject`). It also enforces strict alignment for both DKIM and SPF (`adkim=s; aspf=s`). Aggregate reports are sent to `dmarc-aggregate@example.com`, and forensic reports are sent to `dmarc-forensic@example.com`. Forensic reports are triggered by any authentication failure (`fo=1`). This is a strong DMARC configuration suitable for organizations with mature email authentication practices.

Understanding DMARC Alignment

DMARC alignment refers to the relationship between the domain used in the “From” header of the email and the domains used in the SPF and DKIM authentication checks. DMARC requires either SPF or DKIM to “align” with the “From” domain for the email to pass DMARC authentication.

There are two types of alignment: strict and relaxed.

• Strict Alignment: For DKIM, the “d=” tag in the DKIM signature must exactly match the domain in the “From” header. For SPF, the domain used to perform the SPF check must exactly match the domain in the “From” header.
• Relaxed Alignment: For DKIM, the “d=” tag in the DKIM signature must be a subdomain of the domain in the “From” header. For SPF, the domain used to perform the SPF check must be the same as or a subdomain of the domain in the “From” header.

The alignment mode is specified using the adkim and aspf tags in the DMARC record. The default alignment mode is relaxed.

Strict alignment provides stronger protection against spoofing, but it can also be more difficult to configure correctly. Relaxed alignment is more forgiving but provides less protection against spoofing.

Analyzing DMARC Reports

DMARC reports provide valuable insights into your email authentication ecosystem. There are two types of DMARC reports:

• Aggregate Reports: These reports provide a summary of email authentication results, including the number of emails that passed and failed SPF and DKIM, the DMARC policy applied, and the source IP addresses of the emails. Aggregate reports are typically sent daily or weekly and are in XML format.
• Forensic Reports: These reports provide detailed information about individual email authentication failures, including the full email headers and body. Forensic reports are typically sent in real-time and can contain personally identifiable information (PII). Use with caution and ensure compliance with privacy regulations.

Analyzing DMARC reports can help you identify and troubleshoot email authentication issues, detect potential spoofing attacks, and fine-tune your DMARC policy.

There are various tools available to help you analyze DMARC reports, including online DMARC report analyzers and commercial DMARC monitoring services.

DMARC reports can be initially challenging to parse due to their XML format. Many online tools can help convert these XML reports into more readable formats and provide insightful analysis. Examples include:

• dmarcian’s DMARC Report Analyzer
• EasyDMARC’s DMARC Report Analyzer
• Agari Brand Protection

These tools help visualize the data, identify trends, and pinpoint any issues with your email authentication setup. They can highlight sources of unauthorized email, identify misconfigured SPF or DKIM records, and provide actionable insights to improve your email deliverability and security.

By implementing DMARC, you can gain greater control over your email ecosystem, protect your brand from spoofing attacks, and improve your email deliverability rates.

Testing and Monitoring Your Email Authentication

Implementing SPF, DKIM, and DMARC is just the first step. It’s crucial to continuously test and monitor your email authentication configuration to ensure it’s working correctly and to identify any potential issues that may arise.

Regular testing helps you proactively identify misconfigurations or changes that could impact your email deliverability. Monitoring allows you to track your email authentication results over time, detect potential spoofing attempts, and fine-tune your policies.

Testing Your SPF and DKIM Configuration

There are several ways to test your SPF and DKIM configuration:

• Using Online Email Authentication Checkers: Several online tools can check your SPF and DKIM configuration by sending an email to a designated address and analyzing the email headers.
• Manually Analyzing Email Headers: You can manually analyze the email headers of emails sent from your domain to check for SPF and DKIM pass/fail results.
• Using Command-Line Tools: You can use command-line tools like dig and nslookup to query your DNS records and verify that your SPF and DKIM records are configured correctly.

Example 1: Using an online email authentication checker (Mail-Tester.com)

1. Go to Mail-Tester.com.
2. Copy the unique email address provided on the website.
3. Send an email from your domain to the provided email address.
4. Click the “Then check your score” button on Mail-Tester.com.
5. Mail-Tester.com will analyze your email and provide a score and detailed report of your email authentication results, including SPF, DKIM, and DMARC.