This paper presents a specific man-in-the-middle exploit: Ambient Tactical Deception (ATD) in online communication, realized via a malicious web browser extension. Extensions manipulate web content in unobtrusive ways as ambient intermediaries of the overall browsing experience. In our previous work, we demonstrated that it is possible to employ tactical deception by making covert changes in the text content of a web page, regardless of the source. In this work, we investigated the application of ATD in a web-based email discourse where the objective is to manipulate the interpersonal perception without the knowledge of the involved parties. We focus on web-based email text because it is asynchronous and usually revised for clarity and politeness. Previous research has demonstrated that people's perception of politeness in online communication is based on three factors: the degree of imposition, the power of the receiver over the sender, and the social distance between them. We interviewed participants about their perception of these factors to establish the plausibility of ATD for email discourse. The results indicate that by covertly altering the politeness strategy in an email, it is possible for an ATD attacker to manipulate the receiver's perception on all of the politeness factors. Our findings support the Brown and Levinson's politeness theory and Walther's hyperpersonal model of email communication.