This study reports on several typical scenarios of the use of email interface agents under the influence of critical incidents. The critical incident technique was employed to survey the actual users of an interface agent-based email notification application. Respondents were asked to provide the last most significant either positive or negative incident of the usage of interface agents in their email application, and sixty critical incidents were obtained. With regards to positive-outcome situations, one representative scenario was constructed. With respect to the negative-outcome events, three distinct scenarios were identified. Overall, it is concluded that users acknowledge the quality of an agent when it acts reliably, marketers should advertise only realistic agent capabilities, an agent’s intrusive behavior results in an immediate agent usage termination, operability issues sometimes force people to reject the technology, and users attempt to preserve the employment of an agent under the negative impacts of external factors.