Why is Mimecast causing DKIM body hash failures?

Email marketer from MXToolbox suggests that Mimecast's handling of ARC (Authenticated Received Chain) signatures, when forwarding mail can sometimes cause problems. If Mimecast isn't properly preserving ARC signatures, it can impact DKIM verification.

Email marketer from Stack Overflow suggests that differences in MIME encoding between the sender and Mimecast could lead to DKIM failures. Specifically, different line endings or character encodings can alter the body hash.

Email marketer from Email Testing Blog advises contacting Mimecast support to perform thorough testing and troubleshooting. They can help identify the specific causes of DKIM failures and provide guidance on resolving the issue.

Email marketer from Reddit suggests that Mimecast's URL rewriting feature, which replaces original URLs with Mimecast's tracking URLs, might be the cause of DKIM failures. This is because rewriting the URL changes the email body, thus invalidating the DKIM signature.

Email marketer from Email Deliverability Blog states that Mimecast, like many security appliances, may modify email content for security purposes. Actions like adding disclaimers, converting HTML to plain text, or removing active content can alter the message body, thus causing DKIM to fail. It's crucial to understand these potential changes and configure Mimecast to minimize impact on DKIM.

Email marketer from Super User explains that incorrect character encoding by Mimecast can alter the email body and cause DKIM failures. Specifically, if an email is sent in UTF-8 and Mimecast converts it to ASCII, this can break the DKIM signature.

Email marketer from Email Security Tips recommends reviewing Mimecast's quarantine settings to ensure that legitimate emails are not being quarantined due to DKIM failures. Incorrect quarantine settings can lead to false positives and impact email delivery.

Email marketer from EmailGeeks Forum mentions that Mimecast sometimes adds footers to emails for branding or compliance purposes. If these footers are added after the DKIM signature is calculated, it will cause a DKIM failure.

Email marketer from Email Marketing Community mentions that Mimecast could be manipulating the email content to scan for phishing attempts or malware, inadvertently causing DKIM failures. This is often due to how the content is altered during the scanning process.

Email marketer from Tech Support Forum advises checking Mimecast's configuration settings to ensure that DKIM verification is properly enabled and configured. Incorrect settings or misconfigured policies can lead to DKIM failures, even if the email is properly signed by the sender.

Expert from Word to the Wise, Laura Atkins, explains that Mimecast, being a security service, often modifies email content, which can inadvertently cause DKIM body hash failures. This includes actions such as URL rewriting, adding footers or disclaimers, or converting HTML to plain text. These alterations change the message body, invalidating the DKIM signature.

Expert from Word to the Wise, Laura Atkins, explains that the most likely cause of a DKIM failure is because the body hash did not verify because the email was altered. Mimecast will at times alter the body of an email and this will lead to DKIM failure.

Expert from Email Geeks shares that their internal tool was showing a lot of DKIM failures recently, even on generic mail. They ended up switching DKIM libraries which could be the cause of Mimecast's issues if they are using the same library.

Documentation from OpenDKIM explains that different DKIM implementations might handle body hash calculations differently (e.g., using different canonicalization algorithms or handling whitespace in different ways). This can lead to DKIM failures if the sender and Mimecast are using different implementations.

Documentation from Mimecast explains that if Mimecast modifies the content of an email during processing (e.g., adding a disclaimer, removing attachments, or converting the format), it can cause the DKIM signature to fail verification. This is because the DKIM signature is calculated based on the original content of the email, and any changes will invalidate the signature.

Documentation from RFC 6376 (DKIM specification) clarifies that any modification to the email body after DKIM signing will cause the DKIM verification to fail. This includes changes to whitespace, line endings, or character encoding.

Documentation from DKIM.org explains DKIM signatures are based on the email header and body, which can be broken if the body is changed in transit. Any modifications to the body will result in a DKIM verification failure.

Documentation from Authlogic explains message signing practices, by making sure that message signing is done as one of the last steps to avoid tampering.