What type of email signature offers the highest level of security?

A digital signature provides the highest level of security among the different types of email signatures. This is because a digital signature uses cryptographic techniques to ensure that the message has not been altered in transit and verifies the identity of the sender. When an email is sent with a digital signature, it is accompanied by an encrypted version of the sender's identity, which recipients can verify using a public key.

This verification process helps protect against forgery and ensures that the message is genuinely from the claimed sender. Unlike plain text and HTML signatures, which do not provide any authentication or integrity checks, a digital signature combines these elements, creating a secure method of communication. Additionally, although an image signature may be visually appealing, it can easily be reproduced and does not offer any security features such as authentication or data integrity, making it less secure than a digital signature.