Most people live under the assumption that email is immutable once delivered, like a physical letter. A new email exploit, dubbed ROPEMAKER by Mimecast’s research team, turns that assumption on its head, undermining the security and non-repudiation of email; even for those that use SMIME or PGP for signing. Using the ROPEMAKER exploit a malicious actor can change the displayed content in an email at will. For example, a malicious actor could swap a benign URL with a malicious one in an email already delivered to your inbox, turn simple text into a malicious URL, or edit any text in the body of an email whenever they want. All of this can be done without direct access to the inbox.