Techniques are described for automatically identifying and inhibiting suspect electronic communications between users, such as for electronic communications that may reflect fraudulent activities by one or more of the users or that are otherwise inappropriate for one or more reasons. In some situations, the communications may relate to transactions in which the users are involved, such as for users that are buyers and sellers of items interacting via one or more electronic marketplaces. The communications may occur via a communication mechanism provided by an electronic marketplace that acts as an intermediary between the sender of a communication and the one or more intended recipients of the communication. The automatic identification of suspect communications that may be inappropriate includes automatically assessing the communications in one or more ways, and identified suspect communications and any associated inappropriate user activities may be inhibited in various ways.