What is DKIM oversigning, how does it work, and why is it important for email authentication?

Email marketer from EmailOnAcid shares that using DKIM, with techniques like oversigning, strengthens email authentication, making it more difficult for spammers and phishers to impersonate legitimate senders and improving overall email security.

Email marketer from StackExchange explains that DKIM oversigning is used to validate the integrity of email headers, which is particularly important for preventing header injection attacks and maintaining the trustworthiness of email communications.

Email marketer from Proofpoint explains that DKIM helps to prevent email fraud and phishing attacks by verifying the authenticity of email senders, protecting recipients from malicious emails and ensuring trust in email communications.

Email marketer from SendGrid shares that implementing DKIM helps improve email deliverability by building trust with mailbox providers, ensuring that legitimate emails reach their intended recipients and reducing the likelihood of being marked as spam.

Email marketer from ZeroBounce explains that DKIM is essential for maintaining a positive sender reputation, ensuring that email campaigns are delivered successfully and improving overall email marketing performance by reducing bounce rates and improving engagement.

Email marketer from Mailhardener explains that DKIM oversigning involves signing the same header field multiple times to protect against header manipulation, ensuring that malicious actors cannot insert or modify header fields without invalidating the DKIM signature.

Email marketer from Email Marketing Forum responds that DKIM is important because it provides a cryptographic signature that validates the origin and integrity of email messages, helping recipients identify legitimate senders and combat phishing scams.

Marketer from Email Geeks shares that oversigning works because the hashes are calculated using the existing header and a second, null, header. If attackers replay and add a second header, the hashes won’t validate.

Email marketer from Reddit shares that DKIM oversigning provides an extra layer of security by making it harder for attackers to inject malicious headers into email messages. It's a way to be more certain that the headers haven't been tampered with during transit.

Expert from Email Geeks explains that if fields like To: and CC: appear more than once in the DKIM h= field, it's for oversigning. The second TO: means if bad actors add a second to: field, it might cause a DMARC failure due to a DKIM signature mismatch.

Expert from Spam Resource explains that a valid DKIM record is limited to 512 bytes, and may be as little as 255, depending on your DNS provider. Using multiple DKIM records will help prevent you going over those limits, so is important to consider

Expert from Email Geeks responds that DKIM signature invalidation is more about ensuring signatures are invalidated if headers are changed than DMARC itself, but the layering semantics are crucial.

Expert from Word to the Wise shares that setting up DKIM is a complicated but valuable tool. The first step is to create a key pair, then you need to add the public key to your DNS records, and configure your mail server to sign outgoing emails with the private key. This is an important step to follow.

Documentation from DMARC.org explains that DKIM is a crucial component of DMARC (Domain-based Message Authentication, Reporting & Conformance), which helps domain owners protect their brands from email spoofing and phishing attacks by specifying how email receivers should handle messages that fail authentication checks.

Documentation from AuthSMTP describes that DKIM signing, which can include oversigning, is crucial for improving email deliverability by authenticating the sender's domain, reducing the chances of emails being marked as spam or phishing attempts.

Documentation from Red Sift shares that DKIM oversigning enhances security by validating that headers have not been tampered with. It ensures that alterations to signed headers will break the DKIM signature, preventing spoofing and phishing attacks.

Documentation from ietf.org explains that DKIM (DomainKeys Identified Mail) allows signing email messages such that recipients can verify the sender's domain and that the message content has not been altered during transit. Oversigning, though not explicitly named, aligns with the standard's goal of authenticating message headers and body.

Documentation from Microsoft responds that DKIM, in conjunction with SPF (Sender Policy Framework) and DMARC, provides a comprehensive email authentication framework, helping organizations protect their email domains from spoofing and phishing attacks and ensuring secure email communication.