A client computing system sends to a server system a presentation request for an audio presentation of electronic communications, and receives a manifest from the server system. The manifest indicates a plurality of segment-specific retrieval locations in which a different one of the plurality of segment-specific retrieval locations is indicated for each of a plurality of text-to-speech audio segments of the audio presentation. For each of the plurality of text-to-speech audio segments, the client computing system identifies a presentation order of the text-to-speech audio segment within the audio presentation; sends to the server system a segment request for the text-to-speech audio segment at the segment-specific retrieval location for that text-to-speech audio segment; receives from the server system the text-to-speech audio segment responsive to the segment request for that text-to-speech audio segment; and outputs the text-to-speech audio segment in the identified presentation order.