Email signing, also known as email authentication or digital signing, is a process used to verify the authenticity and integrity of an email message. It is a way to ensure that an email comes from the claimed sender and has not been tampered with during transmission. Email signing uses cryptographic techniques to add a digital signature to the email message.

Here’s how email signing typically works:

Digital Signature Generation: The sender’s email client or server uses a private key to generate a unique digital signature for the email message. The private key is a piece of cryptographic information known only to the sender and is used to create the signature.

Public Key Publication: The sender’s public key is usually stored in a digital certificate, which may be provided by a Certificate Authority (CA) or self-signed. This public key is used by the recipient to verify the digital signature.

Appending the Signature: The digital signature, along with some metadata about the signing process, is appended to the email message.

Sending the Signed Email: The signed email is sent to the recipient.

Verification by Recipient: When the recipient’s email client or server receives the signed email, it uses the sender’s public key (retrieved from the digital certificate) to verify the authenticity of the digital signature. If the signature matches the content of the email and the sender’s public key, it indicates that the email has not been altered in transit and is genuinely from the claimed sender.

Email signing is primarily achieved using cryptographic algorithms, such as asymmetric encryption (RSA or ECC), and digital certificates (like X.509). Common email signing standards include DKIM (DomainKeys Identified Mail) and S/MIME (Secure/Multipurpose Internet Mail Extensions).

By using email signing, organizations, and individuals can protect against email spoofing and man-in-the-middle attacks. It helps recipients identify genuine communications from trusted senders and avoid falling victim to phishing scams.