It has long been established that many workplace tasks are managed through email communication, and that these tasks involve the exchange of requests and commitments. Users would be better able to manage and monitor tasks in their email if systems could identify the utterances which place responsibility for action on themselves or others. Such systems require a robust understanding of which utterances convey requests and commitments. Previous attempts to classify similar phenomena in email have mostly been at the message level and have lacked detailed and robust category definitions that allow unambiguous classification at the utterance level. To address this gap, this paper presents precise definitions for classifying requests and commitments in email, based on concepts from Speech Act Theory, and informed by the results of two independent manual annotation experiments using data from the Enron email corpus. The specific surface realisation of requests and commitments in email are also considered, with the aim of clarifying how a range of potentially difficult cases should be dealt with. This paper thus contributes a well-grounded definitional basis for the classification of task-oriented speech acts in email.