20 September 2026 · DMARC Engine · 36 min read
Introduction to Auto-Forwarding and DKIM Failures
Auto-forwarding, a feature commonly used to redirect emails from one address to another, can have a significant impact on Domain-based Message Authentication, Reporting, and Conformance (DMARC) validation, particularly with regards to DomainKeys Identified Mail (DKIM) signatures. In our experience managing DMARC, SPF, DKIM, MTA-STS, and BIMI for customers, we have seen firsthand how auto-forwarding can lead to DKIM signature failures, resulting in DMARC failures and potentially causing emails to be flagged as spam or rejected outright.
When an email is auto-forwarded, the forwarding server often modifies the email headers, which can invalidate the DKIM signature. This is because DKIM signatures are generated based on the email's headers and body, and any changes to these components can cause the signature to fail verification. For example, if an email is forwarded from a user's mailbox to an external address, the forwarding server may add a Received header or modify the From header, which can break the DKIM signature.
In a hosted or managed setup, such as the one we operate at DMARC Engine, we have seen that auto-forwarding can be a common cause of DKIM signature failures. Our customers often configure auto-forwarding rules to redirect emails from one address to another, without realising the potential impact on DMARC validation. To mitigate this issue, we recommend that customers carefully review their auto-forwarding configurations and consider using techniques such as rewriting the From header or using a DKIM proxy server to preserve the DKIM signature.
To illustrate the impact of auto-forwarding on DKIM signatures, consider the following example. Suppose we have an email with a DKIM signature generated by the sending domain example.com. The email is then auto-forwarded by the receiving server to an external address, resulting in the addition of a Received header:
Received: from mail.example.com (mail.example.com [192.0.2.1])
by forwarder.example.net (Postfix) with ESMTP id 1234567890
for <user@example.net>; Thu, 01 Jan 2020 12:00:00 +0000The resulting email may still contain the original DKIM signature, but the addition of the Received header can cause the signature to fail verification. In our experience, this can result in a DMARC failure, even if the email is otherwise legitimate.
In some cases, email clients may also modify the email headers or body during the auto-forwarding process, which can further exacerbate the issue. For example, some email clients may add a X-Forwarded-For header or modify the Subject header, which can break the DKIM signature. To optimise DKIM signature preservation during auto-forwarding, it is essential to carefully review the email client configurations and consider using techniques such as DKIM signing at the email client level or using a DKIM proxy server.
Our analysis of aggregate reports has shown that auto-forwarding is a common cause of DKIM signature failures, particularly in cases where the forwarding server modifies the email headers or body. To centre our efforts on mitigating this issue, we recommend that email administrators carefully review their auto-forwarding configurations and consider implementing techniques to preserve the DKIM signature. In the next section, we will delve deeper into the impact of auto-forwarding on DKIM signatures and explore common email client configurations that can affect DKIM signature preservation.
In real-world scenarios, the colour of the email client's auto-forwarding configuration can significantly impact the DKIM signature preservation. For instance, some email clients may have a more aggressive auto-forwarding configuration, which can result in a higher likelihood of DKIM signature failures. To organise and streamline the process of preserving DKIM signatures during auto-forwarding, we recommend that email administrators develop a comprehensive understanding of their email client configurations and implement strategies to mitigate the impact of auto-forwarding on DMARC validation.
By understanding the intricacies of auto-forwarding and its impact on DKIM signatures, email administrators can take proactive steps to preserve the integrity of their emails and maintain a high level of deliverability. In our experience, a well-organised and carefully planned approach to email client configuration can significantly reduce the likelihood of DKIM signature failures due to auto-forwarding, resulting in improved email deliverability and a better overall email experience for users.
To further illustrate the impact of auto-forwarding on DKIM signatures, consider the following example of a DKIM signature that has failed verification due to auto-forwarding:
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=selector; t=1234567890;
bh=examplehash;
h=From:To:Subject;
b=examplebase64encodedsignatureIn this example, the DKIM signature has failed verification due to the addition of a Received header during the auto-forwarding process. To preserve the DKIM signature, the email administrator could consider using a DKIM proxy server or rewriting the From header to maintain the integrity of the email. By taking a proactive approach to email client configuration and DKIM signature preservation, email administrators can optimise their email deliverability and maintain a high level of trust with their users.
In our experience, the key to preserving DKIM signatures during auto-forwarding is to carefully review and optimise the email client configurations. By understanding the intricacies of auto-forwarding and its impact on DKIM signatures, email administrators can develop a comprehensive strategy to mitigate the issue and maintain a high level of email deliverability. In the next section, we will explore the impact of auto-forwarding on DKIM signatures in more detail, and discuss common email client configurations that can affect DKIM signature preservation.
By examining the specifics of auto-forwarding and its impact on DKIM signatures, email administrators can develop a nuanced understanding of the issue and implement effective strategies to preserve the integrity of their emails. In our experience, a well-pl
Understanding the Impact of Auto-Forwarding on DKIM Signatures
When a message is auto-forwarded, the email client or server often modifies the message in some way, which can cause the DKIM signature to fail verification. This is because the DKIM signature is generated based on the content of the message, including the headers and body, and any changes to this content can cause the signature to no longer match. In our experience, one of the most common causes of DKIM signature failures is auto-forwarding, particularly when the forwarding server or client adds or modifies headers, or alters the message body in some way.
For example, consider a message that is signed with a DKIM signature using the relaxed/relaxed canonicalisation algorithm, which is a common choice for its balance between security and flexibility. If this message is then auto-forwarded by a server that adds a Received header, the DKIM signature will fail verification because the added header changes the content of the message. This can be seen in the following example, where the original message has a DKIM signature with the following properties:
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=selector1; t=1643723900;
bh=...;
h=From:To:Subject;
b=...If the message is then auto-forwarded by a server that adds a Received header, the resulting message might look like this:
Received: from mailserver.example.com (mailserver.example.com [192.0.2.1])
by forwarder.example.net (Postfix) with ESMTP id 1234567890
for <recipient@example.net>; Thu, 27 Jan 2022 14:30:00 +0000
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=selector1; t=1643723900;
bh=...;
h=From:To:Subject;
b=...In this case, the added Received header changes the content of the message, causing the DKIM signature to fail verification.
Another common issue we see is when email clients or servers modify the message body, for example by adding or removing whitespace, or by converting the message from one format to another (e.g. from HTML to plain text). This can also cause the DKIM signature to fail verification, because the signature is generated based on the original content of the message.
In a hosted or managed setup, such as the one we operate at DMARC Engine, we often see customers struggling with DKIM signature failures due to auto-forwarding. To mitigate this, we recommend that customers configure their email clients and servers to preserve the DKIM signature when forwarding messages. This can typically be done by configuring the client or server to use a canonicalisation algorithm that is more tolerant of modifications, such as relaxed/relaxed, or by using a DKIM signature that is generated using a more robust algorithm, such as rsa-sha512.
It's also worth noting that some email clients and servers may have specific settings or configurations that can help preserve the DKIM signature when forwarding messages. For example, some clients may have an option to "preserve headers" or "forward without modification", which can help prevent the DKIM signature from being invalidated. In our experience, these settings can be tricky to find and configure, and may require some experimentation to get right.
In terms of specific recommendations, we suggest that email administrators take the following steps to optimise their email client configurations and preserve DKIM signatures:
- Use a canonicalisation algorithm that is more tolerant of modifications, such as
relaxed/relaxed. - Use a DKIM signature that is generated using a more robust algorithm, such as
rsa-sha512. - Configure email clients and servers to preserve headers and message content when forwarding messages.
- Test and verify that DKIM signatures are being preserved correctly, using tools such as aggregate reports or DKIM verification software.
By following these recommendations, email administrators can help ensure that their DKIM signatures remain valid and intact, even when messages are auto-forwarded. This can help improve the overall security and deliverability of their email, and reduce the risk of messages being flagged as spam or rejected by recipient servers.
Common Email Client Configurations and Their Effects on DKIM
The way email clients are configured can significantly impact the integrity of DKIM signatures during auto-forwarding. In our experience, the colour of the DKIM signature validation can change from a pleasant green to a worrying red due to the way email clients handle forwarded emails. For instance, when using Microsoft Outlook, the auto-forwarding feature can modify the email headers, which in turn can cause the DKIM signature to fail validation. This is because Outlook, by default, adds a X-MS-Exchange-Organized-Store-MessageToken header, which alters the signature.
To mitigate this, we recommend configuring Outlook to preserve the original headers during auto-forwarding. This can be achieved by setting the ForwardAsAttachment option to True, which will forward the email as an attachment, thus preserving the original headers and the DKIM signature.
On the other hand, email clients like Mozilla Thunderbird handle auto-forwarding differently. Thunderbird, by default, will rewrite the From header, which can cause the DKIM signature to fail validation. However, this behaviour can be changed by configuring Thunderbird to use the forward as option, which will preserve the original From header.
Here is an example of how the forward as option can be configured in Thunderbird:
# Thunderbird configuration file
[Mail]
forward_as = trueIn a hosted or managed setup, such as the one provided by DMARC Engine, the centre of attention is on optimising the email client configurations to preserve DKIM signatures. Our team works closely with customers to configure their email clients to use the correct settings, thus ensuring that DKIM signatures remain intact during auto-forwarding.
Another email client that requires special attention is Gmail. Gmail's auto-forwarding feature can cause the DKIM signature to fail validation due to the way it handles email headers. Specifically, Gmail adds a X-Forwarded-For header, which can alter the DKIM signature. To mitigate this, we recommend configuring Gmail to use the forward as option, which will preserve the original headers and the DKIM signature.
Here is an example of how the X-Forwarded-For header can cause the DKIM signature to fail validation:
# Example of a DKIM signature failure due to X-Forwarded-For header
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=selector; t=1643723900;
bh=...;
h=From:To:Subject:MIME-Version:Content-Type;
b=...
X-Forwarded-For: example@gmail.com
# DKIM validation result
DKIM verification failedIn this example, the X-Forwarded-For header added by Gmail causes the DKIM signature to fail validation. To avoid this, we recommend configuring Gmail to use the forward as option, which will preserve the original headers and the DKIM signature.
In addition to email client configurations, the way auto-forwarding rules are set up can also impact DKIM signatures. For instance, when using Microsoft Exchange, the auto-forwarding rules can be set up to preserve the original headers and the DKIM signature. However, this requires careful configuration of the TransportRule settings.
Here is an example of how the TransportRule settings can be configured to preserve DKIM signatures:
# Example of TransportRule settings to preserve DKIM signatures
New-TransportRule -Name "Preserve DKIM" -RuleType ModifyMessage -Priority 0 `
-SetHeaderName "X-Preserve-DKIM" -SetHeaderValue "True" `
-ExceptIfHeaderContainsWords $null -ExceptIfHeaderDoesNotContainWords $null `
-ExceptIfFrom $null -ExceptIfFromMemberOf $null -ExceptIfTo $null `
-ExceptIfToMemberOf $null -ApplyHtmlDisclaimerLocation $null `
-ApplyHtmlDisclaimerText $null -ApplyHtmlDisclaimerFallbackAction $null `
-RemoveHeader $null -SetSCL $null -SetSpamConfidenceLevel $null `
-RemoveOME $null -ApplyOME $null -GenerateIncidentReport $null `
-StopRuleProcessing $falseIn short, the way email clients are configured can significantly impact the integrity of DKIM signatures during auto-forwarding. By understanding the specific configurations and settings required for each email client, email administrators can take steps to preserve DKIM signatures and ensure that emails are delivered correctly. In a hosted or managed setup, such as the one provided by DMARC Engine, our team works closely with customers to configure their email clients to use the correct settings, thus ensuring that DKIM signatures remain intact during auto-forwarding.
Operational Guidance for Configuring Email Clients to Preserve DKIM Signatures
When it comes to configuring email clients to preserve DKIM signatures, the centre of attention should be on the handling of auto-forwarding rules. Auto-forwarding, while convenient for users, can significantly impact the integrity of DKIM signatures, leading to verification failures and potential delivery issues. In our experience with managing DMARC, SPF, DKIM, MTA-STS, and BIMI for customers, we have observed that the way email clients handle auto-forwarding can make all the difference in maintaining DKIM signature integrity.
To optimise DKIM signature preservation during auto-forwarding, email administrators must carefully consider the configuration of their email clients. One key aspect is the use of the dkim-signature header. When an email is auto-forwarded, the email client may modify the message in a way that invalidates the DKIM signature. For instance, if the client adds a prefix to the subject line or modifies the message body, the DKIM signature will fail verification.
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=selector1; t=1643723900;
bh=...;
h=From:To:Subject:MIME-Version:Content-Type;
b=...In the above example, the h tag specifies the headers that are included in the DKIM signature. If the email client modifies any of these headers during auto-forwarding, the DKIM signature will fail. To mitigate this, email administrators can configure their clients to preserve the original headers and message body during auto-forwarding. This can typically be achieved through the client's settings or by using a plugin that specifically handles DKIM signature preservation.
Another crucial factor is the colour of the DKIM alignment. In DMARC, alignment refers to the relationship between the domain in the From header and the domain in the DKIM signature. If these domains do not align, the DMARC check will fail, even if the DKIM signature itself is valid. When configuring email clients for auto-forwarding, it is essential to ensure that the client does not modify the From header or the DKIM signature in a way that would cause alignment issues.
In a hosted or managed setup, such as the one we operate at DMARC Engine, handling DKIM signature preservation during auto-forwarding can be more complex due to the variety of email clients and configurations involved. To address this, we employ a combination of technical measures, including the use of DKIM key management and automated DKIM signature verification. This allows us to monitor and maintain the integrity of DKIM signatures across different email clients and configurations.
For email administrators, one of the trade-offs to consider is the balance between user convenience and email security. While auto-forwarding can be a useful feature for users, it can also introduce security risks if not properly configured. To navigate this trade-off, administrators can consider implementing alternative solutions, such as server-side forwarding rules, which can help maintain DKIM signature integrity while still providing users with the functionality they need.
In terms of specific configuration steps, the process will vary depending on the email client being used. For example, in Microsoft Outlook, administrators can configure auto-forwarding rules to preserve the original message headers and body. Similarly, in Mozilla Thunderbird, there are extensions available that can help preserve DKIM signatures during auto-forwarding.
# Example of a preserved DKIM signature in an auto-forwarded email
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=selector1; t=1643723900;
bh=...;
h=From:To:Subject:MIME-Version:Content-Type;
b=...
X-Forwarded-For: user@example.comIn this example, the X-Forwarded-For header indicates that the email was forwarded, but the DKIM signature remains intact, thanks to proper configuration of the email client.
Ultimately, the key to preserving DKIM signatures during auto-forwarding is careful configuration and monitoring of email clients. By understanding the specific requirements and limitations of each client, email administrators can take steps to optimise DKIM signature preservation and maintain the security and integrity of their email communications. At DMARC Engine, we work closely with our customers to ensure that their email configurations are optimised for DKIM signature preservation, providing them with the tools and expertise needed to navigate the complexities of email authentication and security.
Real-World Examples of DKIM Signature Failures Due to Auto-Forwarding
In our experience managing DMARC, SPF, DKIM, MTA-STS, and BIMI for customers, we have encountered numerous instances where auto-forwarding has led to DKIM signature failures. These failures can be attributed to the alteration of the email's body or headers during the forwarding process, which invalidates the DKIM signature. For instance, when an email client auto-forwards a message, it may modify the message headers, such as adding a X-Forwarded-For header, or alter the message body, such as adding a forwarding notice. These modifications can cause the DKIM signature verification to fail, as the signature is generated based on the original message.
A concrete example of this can be seen in the following email header snippet:
Received: from mail.example.com (mail.example.com [192.0.2.1])
by mx.google.com with ESMTPS id p10si1181582ioj.87.2023.02.20.14.30.00
for <recipient@example.net>
(version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256)
Mon, 20 Feb 2023 14:30:00 +0000
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=selector1; t=1676889000;
bh=...;
h=From:To:Subject:MIME-Version:Content-Type;
b=...
X-Forwarded-For: auto-forward@example.comIn this example, the email client has added an X-Forwarded-For header, which was not present in the original message. This modification causes the DKIM signature verification to fail, as the signature was generated based on the original message headers.
Another example is when an email client auto-forwards a message and modifies the message body, such as adding a forwarding notice. This can be seen in the following email body snippet:
---------- Forwarded message ----------
From: sender@example.com
To: recipient@example.net
Subject: Test Email
This is a test email.
---
Auto-forwarded by auto-forward@example.comIn this example, the email client has added a forwarding notice to the message body, which was not present in the original message. This modification causes the DKIM signature verification to fail, as the signature was generated based on the original message body.
To mitigate these issues, it is essential to configure email clients to preserve DKIM signatures during auto-forwarding. One approach is to use a hosted or managed setup, such as DMARC Engine, which can handle DKIM signature verification and reporting on behalf of the customer. This can help to simplify the process of managing DKIM signatures and reduce the risk of signature failures due to auto-forwarding.
In a hosted setup, the email service provider can configure their systems to preserve DKIM signatures during auto-forwarding. For example, they can use a technique called "DKIM signature rewriting" to update the DKIM signature to reflect the changes made to the message during forwarding. This can help to ensure that the DKIM signature remains valid, even after the message has been forwarded.
However, in some cases, DKIM signature rewriting may not be possible or may not be effective. For instance, if the email client modifies the message body in a way that cannot be predicted or accounted for, it may not be possible to update the DKIM signature accordingly. In such cases, it may be necessary to use alternative approaches, such as using a different authentication mechanism, such as SPF or BIMI.
In our experience, the key to successfully preserving DKIM signatures during auto-forwarding is to carefully configure email clients and servers to minimise modifications to the message. This can involve configuring email clients to use a specific forwarding method, such as using a mail command or a forwarding agent, rather than modifying the message body or headers directly. Also, it is essential to monitor DKIM signature verification reports and adjust the configuration as needed to ensure that signatures remain valid.
To illustrate this, consider the following example of a DKIM signature verification report:
<feedback>
<version>1</version>
<record>
<row>
<source_ip>192.0.2.1</source_ip>
<count>10</count>
<policy_evaluated>
<disposition>none</disposition>
<dkim>fail</dkim>
<spf>pass</spf>
</policy_evaluated>
</row>
</record>
</feedback>In this example, the report indicates that the DKIM signature verification failed for 10 messages from the IP address 192.0.2.1. This suggests that there may be an issue with the email client or server configuration that is causing the DKIM signature to fail. By analysing the report and adjusting the configuration accordingly, it is possible to improve the effectiveness of DKIM signature verification and reduce the risk of signature failures due to auto-forwarding.
In short, preserving DKIM signatures during auto-forwarding requires careful configuration of email clients and servers to minimise modifications to the message. By using a hosted or managed setup, configuring email clients to preserve DKIM signatures, and monitoring DKIM signature verification reports, it is possible to reduce the risk of signature failures and improve the effectiveness of DMARC and email authentication.
Aggregate Report Analysis: Identifying DKIM Signature Failures
Analysing aggregate reports is a crucial step in identifying DKIM signature failures caused by auto-forwarding. As a team that hosts and manages DMARC, SPF, DKIM, MTA-STS, and BIMI for customers, we have seen firsthand the importance of closely monitoring these reports to optimise email deliverability. The reports provide valuable insights into the authentication results of emails sent from a domain, including DKIM signature verification failures.
When examining aggregate reports, it is essential to focus on the result field, which indicates the outcome of the DMARC authentication check. A result of none or quarantine may not necessarily be a cause for concern, but a result of fail warrants further investigation. In particular, we look for failures related to DKIM signature verification, which can be caused by auto-forwarding.
For instance, consider the following aggregate report snippet:
{
"org_name": "example.com",
"email": "abuse@example.com",
"extra_contacts": [],
"report_id": "1234567890",
"report_metadata": {
"org_name": "example.com",
"email": "abuse@example.com",
"extra_contacts": [],
"report_id": "1234567890",
"date_range": {
"begin": "2022-01-01T00:00:00Z",
"end": "2022-01-07T23:59:59Z"
}
},
"policy_published": {
"domain": "example.com",
"adkim": "r",
"aspf": "r",
"p": "none",
"sp": "none",
"pct": 100
},
"records": [
{
"row": {
"source_ip": "192.0.2.1",
"count": 10,
"policy_evaluated": {
"disposition": "none",
"dkim": "fail",
"spf": "pass"
}
}
}
]
}In this example, the dkim field has a value of fail, indicating that the DKIM signature verification failed for 10 emails sent from the IP address 192.0.2.1. This failure could be due to auto-forwarding, which altered the email headers and caused the DKIM signature to become invalid.
To identify the root cause of the DKIM signature failure, we need to examine the email headers and the auto-forwarding configuration. In a hosted or managed setup, this process can be automated using scripts and tools that parse the aggregate reports and alert the email administrators to potential issues.
One common issue we encounter is that email clients may not be configured to preserve DKIM signatures during auto-forwarding. For example, some email clients may remove or alter the DKIM-Signature header, causing the verification to fail. To mitigate this issue, email administrators can configure their email clients to use a DKIM signing domain that is different from the parent domain. This approach ensures that the DKIM signature remains valid even after auto-forwarding.
Another challenge is that some email clients may not support DKIM signing or may have limitations on the size of the email that can be signed. In such cases, email administrators may need to use alternative authentication methods, such as SPF or BIMI, to ensure that their emails are authenticated correctly.
In our experience, the key to resolving DKIM signature failures is to carefully analyse the aggregate reports and identify the root cause of the issue. By doing so, email administrators can take targeted actions to optimise their email configuration and ensure that their emails are delivered successfully.
For instance, we worked with a customer who was experiencing a high rate of DKIM signature failures due to auto-forwarding. After analysing the aggregate reports, we discovered that the issue was caused by a misconfigured email client that was removing the DKIM-Signature header during auto-forwarding. We worked with the customer to configure the email client to preserve the DKIM signature, and the issue was resolved.
In another case, we encountered a customer who was using a third-party email service that did not support DKIM signing. We recommended that the customer use a different email service that supported DKIM signing, and we helped them configure the new service to ensure that their emails were authenticated correctly.
In short, aggregate report analysis is a critical step in identifying and resolving DKIM signature failures caused by auto-forwarding. By carefully examining the reports and identifying the root cause of the issue, email administrators can take targeted actions to optimise their email configuration and ensure that their emails are delivered successfully. As a hosted or managed setup, we can provide automated tools and scripts to parse the aggregate reports and alert email administrators to potential issues, making it easier to maintain the integrity of DKIM signatures during auto-forwarding.
To illustrate this point, consider the following example of an aggregate report that shows a high rate of DKIM signature failures:
{
"org_name": "example.com",
"email": "abuse@example.com",
"extra_contacts": [],
"report_id": "1234567890",
"report_metadata": {
"org_name": "example.com",
"email": "abuse@example.com",
"extra_contacts": [],
"report_id": "1234567890",
"date_range": {
"begin": "2022-01-01T00:00:00Z",
"end": "2022-01-07T23:59:59Z"
}
},
"policy_published": {
"domain": "example.com",
"adkim": "r",
"aspf": "r",
"p": "none",
"sp": "none",
"pct": 100
},
"records": [
{
"row": {
"source_ip": "192.0.2.1",
"count": 100,
"policy_evaluated": {
"disposition": "none",
"dkim": "fail",
"spf": "pass"
}
}
},
{
"row": {
"source_ip": "192.0.2.2",
"count": 50,
"policy_evaluated": {
"disposition": "none",
"dkim": "fail",
"spf": "pass"
}
}
}
]
}In this example, the report shows a high rate of DKIM signature failures for emails sent from two different IP addresses. To resolve this issue, we would need to examine the email headers and the auto-forwarding configuration for each IP address to identify the root cause of the problem.
By analysing the aggregate reports and identifying the root cause of the DKIM signature failures, email administrators can take targeted actions to optimise their email configuration and ensure that their emails are delivered successfully. This may involve configuring email clients to preserve DKIM signatures during auto-forwarding, using alternative authentication methods, or working with third-party email services to ensure that they support DKIM signing.
In our experience, the key to maintaining the integrity of DKIM signatures during auto-forwarding is to carefully monitor the aggregate reports and take prompt action to resolve any issues that arise. By doing so, email administrators can ensure that their emails are authenticated correctly and delivered to the intended recipients.
To optimise email deliverability, it is essential to have a thorough understanding of the aggregate reports and the authentication methods used by email clients. By analysing the reports and identifying the root cause of DKIM signature failures, email administrators can take targeted actions to resolve the issues and ensure that their emails are delivered successfully.
In a hosted or managed setup, we can provide automated tools and scripts to parse the aggregate reports and alert email administrators to potential issues, making it easier to maintain the integrity of DKIM signatures during auto-forwarding. Our team can also provide guidance on how to configure email clients to preserve DKIM signatures and how to use alternative authentication methods to ensure that emails are authenticated correctly.
By working together, we can help email administrators optimise their email configuration and ensure that their emails are delivered successfully, even in the presence of auto-forwarding. Our goal is to provide the best possible email deliverability for our customers, and we are committed to helping them resolve any issues that may arise.
In conclusion to this section, aggregate report analysis is a critical step in identifying and resolving DKIM
Trade-Offs and Considerations for Email Administrators
When managing email configurations to optimise DMARC, SPF, and DKIM, administrators must centre their approach around the trade-offs between security, deliverability, and user experience. A key consideration is the impact of auto-forwarding on DKIM signatures, as this can lead to signature failures and affect the overall deliverability of emails. In a hosted or managed setup, such as the one we operate at DMARC Engine, we often see customers struggling to balance these competing demands.
One of the primary trade-offs is between the level of security provided by DKIM and the convenience of auto-forwarding. Strict DKIM configurations can prevent spam and phishing attacks, but may also cause issues with legitimate emails that are auto-forwarded. For example, if a user has set up auto-forwarding from their personal email account to their work email, a strict DKIM policy may cause the forwarded email to fail DMARC, leading to it being quarantined or rejected. In such cases, administrators must weigh the risks and benefits of relaxing their DKIM policies to accommodate auto-forwarding.
Another consideration is the variability in how different email clients handle auto-forwarding and DKIM signatures. Some clients, such as Microsoft Outlook, may modify the email headers or body during forwarding, which can cause DKIM signature failures. In contrast, other clients, such as Mozilla Thunderbird, may preserve the original headers and body, reducing the likelihood of signature failures. Administrators must be aware of these differences and configure their email clients accordingly. For instance, the following record snippet shows how a forwarded email may have its headers modified:
Received: from mail-client.example.com (mail-client.example.com [192.0.2.1])
by mail-server.example.com (Postfix) with ESMTP id 1234567890
for <user@example.com>; Fri, 12 Feb 2023 14:30:00 +0000 (GMT)
X-Forwarded-For: user@example.comIn this example, the X-Forwarded-For header indicates that the email was forwarded, which may cause issues with DKIM signature verification.
To mitigate these issues, administrators can implement various strategies, such as using a relaxed DKIM policy or configuring email clients to preserve the original headers and body during forwarding. However, these approaches may have their own trade-offs, such as reduced security or increased complexity. For example, using a relaxed DKIM policy may allow more spam emails to pass through, while configuring email clients to preserve headers and body may require additional technical expertise.
In a managed setup, such as DMARC Engine, we often recommend a balanced approach that takes into account the specific needs and risks of each customer. This may involve configuring DKIM policies to allow for some flexibility in auto-forwarding, while also implementing additional security measures, such as SPF and DMARC, to prevent spam and phishing attacks. Also, we provide customers with detailed aggregate reports and analysis to help them identify and address DKIM signature failures due to auto-forwarding.
When analysing these reports, administrators should look for patterns and trends that indicate DKIM signature failures, such as a high rate of failures from specific email clients or domains. For instance, the following record snippet shows an example of an aggregate report:
<record>
<row>
<source_ip>192.0.2.1</source_ip>
<count>10</count>
<disposition>fail</disposition>
<dkim>fail</dkim>
<spf>pass</spf>
<domain>example.com</domain>
</row>
</record>In this example, the report indicates that 10 emails from the IP address 192.0.2.1 failed DKIM verification, which may suggest an issue with auto-forwarding or email client configuration.
Ultimately, the key to managing the trade-offs between security, deliverability, and user experience is to adopt a nuanced and flexible approach that takes into account the specific needs and risks of each organisation. By understanding the impact of auto-forwarding on DKIM signatures and implementing strategies to mitigate these issues, administrators can optimise their email configurations to achieve the best possible balance between security and deliverability. In our experience at DMARC Engine, a well-configured email setup can significantly improve deliverability and reduce the risk of spam and phishing attacks, while also providing a better user experience for email recipients.
Step-by-Step Configuration for Popular Email Clients
To optimise email client configuration for DMARC and DKIM, it is crucial to centre on the specific requirements of each client, as the impact of auto-forwarding on DKIM signatures can vary significantly. The following sections provide a step-by-step guide for configuring popular email clients to preserve DKIM signatures during auto-forwarding.
Microsoft Outlook
When configuring Microsoft Outlook for auto-forwarding, it is essential to consider the colour of the authentication results, as a failed DKIM signature can lead to a softfail or hardfail result. To configure Outlook, follow these steps:
1. Open Outlook and navigate to the File menu.
2. Click on the Manage Rules & Alerts button.
3. Select the New Rule option.
4. Choose the Apply rule on messages I receive option.
5. Select the people or public group option.
6. Enter the email address of the recipient.
7. Click on the Next button.
8. Select the forward it to people or public group option.
9. Enter the email address of the forward recipient.
10. Click on the Finish button.
To verify the DKIM signature, use a tool like the dkimpy library in Python:
import dkimpy
# Load the email message
with open('email.eml', 'r') as f:
message = f.read()
# Verify the DKIM signature
result = dkimpy.verify(message)
# Print the result
print(result)In a hosted or managed setup, such as DMARC Engine, the DKIM signature verification is typically handled automatically, and the results are included in the aggregate reports.
Mozilla Thunderbird
Mozilla Thunderbird provides a flexible configuration option for auto-forwarding, which can be used to preserve DKIM signatures. To configure Thunderbird, follow these steps:
1. Open Thunderbird and navigate to the Tools menu.
2. Click on the Message Filters option.
3. Select the New option.
4. Choose the Filter Name option.
5. Enter a name for the filter.
6. Select the Match all of the following option.
7. Choose the From option.
8. Enter the email address of the sender.
9. Click on the + button.
10. Select the Forward To option.
11. Enter the email address of the forward recipient.
To verify the DKIM signature in Thunderbird, use the dkim add-on:
// Load the dkim add-on
const dkim = require('dkim');
// Load the email message
const message = MailUtils.getHeadersForMessage(msgHdr);
// Verify the DKIM signature
const result = dkim.verify(message);
// Print the result
console.log(result);In a hosted or managed setup, the DKIM signature verification is typically handled automatically, and the results are included in the aggregate reports.
Gmail
Gmail provides a simple configuration option for auto-forwarding, which can be used to preserve DKIM signatures. To configure Gmail, follow these steps:
1. Open Gmail and navigate to the Settings menu.
2. Click on the Forwarding and POP/IMAP option.
3. Select the Add a forwarding address option.
4. Enter the email address of the forward recipient.
5. Click on the Next button.
6. Select the Forward a copy of incoming mail to option.
7. Choose the Keep a copy of the message in the inbox option.
To verify the DKIM signature in Gmail, use the Gmail API:
import base64
from googleapiclient.discovery import build
# Load the email message
service = build('gmail', 'v1')
message = service.users().messages().get(userId='me', id='message_id').execute()
# Verify the DKIM signature
dkim_signature = message['payload']['headers'][0]['value']
result = dkimpy.verify(dkim_signature)
# Print the result
print(result)In a hosted or managed setup, such as DMARC Engine, the DKIM signature verification is typically handled automatically, and the results are included in the aggregate reports.
Apple Mail
Apple Mail provides a flexible configuration option for auto-forwarding, which can be used to preserve DKIM signatures. To configure Apple Mail, follow these steps:
1. Open Apple Mail and navigate to the Mail menu.
2. Click on the Preferences option.
3. Select the Rules option.
4. Click on the Add Rule option.
5. Choose the If option.
6. Select the From option.
7. Enter the email address of the sender.
8. Click on the + button.
9. Select the Forward To option.
10. Enter the email address of the forward recipient.
To verify the DKIM signature in Apple Mail, use the dkim command-line tool:
# Load the email message
message=$(cat email.eml)
# Verify the DKIM signature
result=$(dkim -v -f email.eml)
# Print the result
echo $resultIn a hosted or managed setup, the DKIM signature verification is typically handled automatically, and the results are included in the aggregate reports.
Microsoft 365
Microsoft 365 provides a flexible configuration option for auto-forwarding, which can be used to preserve DKIM signatures. To configure Microsoft 365, follow these steps:
1. Open the Microsoft 365 admin centre and navigate to the Mail flow menu.
2. Click on the Rules option.
3. Click on the Add a new rule option.
4. Choose the Apply this rule if option.
5. Select the The sender option.
6. Enter the email address of the sender.
7. Click on the Add action option.
8. Select the Forward the message to option.
9. Enter the email address of the forward recipient.
To verify the DKIM signature in Microsoft 365, use the Get-MessageTrace cmdlet:
# Load the email message
$message = Get-MessageTrace -SenderAddress <sender_address> -RecipientAddress <recipient_address>
# Verify the DKIM signature
$dkim_signature = $message.DkimSignature
$result = Verify-DkimSignature -DkimSignature $dkim_signature
# Print the result
Write-Host $resultIn a hosted or managed setup, such as DMARC Engine, the DKIM signature verification is typically handled automatically, and the results are included in the aggregate reports.
By following these step-by-step guides, email administrators can configure popular email clients to preserve DKIM signatures during auto-forwarding, ensuring that the email messages are delivered to the intended recipients while maintaining the integrity of the DKIM signature. It is essential to note that the configuration steps may vary depending on the specific email client and version, so it is crucial to consult the email client documentation for the most up-to-date information.
Best Practices for Maintaining DKIM Signature Integrity During Forwarding
To optimise DKIM signature integrity during the auto-forwarding process, email administrators must centre their efforts on configuring email clients to preserve the original message headers and body. A crucial step in this process is to ensure that the email client is set up to forward messages without modifying the original content, which can be achieved by using the forward method instead of resend or redirect. This approach helps maintain the original DKIM signature, reducing the likelihood of signature failures during the verification process.
When configuring email clients, it is essential to consider the trade-offs between security and usability. For instance, some email clients may have strict settings that prevent the forwarding of messages with certain types of attachments or content, which can lead to DKIM signature failures. In such cases, email administrators must weigh the benefits of enhanced security against the potential drawbacks of reduced usability.
In a hosted or managed setup, such as the one provided by DMARC Engine, the configuration of email clients is often streamlined to optimise DKIM signature integrity. For example, our managed setup uses a custom configuration that preserves the original message headers and body during the auto-forwarding process, as shown in the following record snippet:
# Custom configuration for preserving DKIM signature integrity
forward_method = "forward"
preserve_headers = true
preserve_body = trueThis configuration ensures that the original DKIM signature is maintained during the auto-forwarding process, reducing the likelihood of signature failures.
Another best practice for maintaining DKIM signature integrity is to use a relaxed canonicalisation algorithm, such as relaxed/relaxed, which allows for minor modifications to the message headers and body without invalidating the DKIM signature. This approach can be particularly useful in scenarios where the email client modifies the message content during the forwarding process.
To illustrate this point, consider the following example of a DKIM signature that uses a relaxed canonicalisation algorithm:
# DKIM signature with relaxed canonicalisation
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.com;
s=selector; t=1643723900;
bh=...;
h=From:To:Subject;
b=...In this example, the relaxed/relaxed canonicalisation algorithm allows for minor modifications to the message headers and body without invalidating the DKIM signature.
In addition to configuring email clients and using relaxed canonicalisation algorithms, email administrators should also monitor their aggregate reports to identify potential issues with DKIM signature integrity. By analysing these reports, administrators can identify patterns of DKIM signature failures and take corrective action to optimise their email client configurations.
For instance, the following aggregate report snippet shows a high rate of DKIM signature failures due to auto-forwarding:
# Aggregate report snippet
{
"org_name": "example.com",
"date": "2022-02-01",
"dkim": {
"fail": 100,
"pass": 500
},
"reason": {
"forwarded": 80
}
}In this example, the high rate of DKIM signature failures due to auto-forwarding indicates that the email client configuration may need to be adjusted to preserve the original message headers and body.
In conclusion to this section, by following these best practices, email administrators can optimise DKIM signature integrity during the auto-forwarding process, reducing the likelihood of signature failures and improving the overall security of their email ecosystem. By centreing their efforts on configuring email clients to preserve the original message headers and body, using relaxed canonicalisation algorithms, and monitoring aggregate reports, administrators can ensure that their DKIM signatures remain valid and effective.