The purpose of this paper is to examine practices of language alternation in email communication among native speakers of Greek and to argue that such practices are a facet of the performative construction of an ‘online’ communicative identity. In the slowly-growing body of literature on linguistic practices in computer-mediated communication (CMC) or computer-mediated discourse (CMD) it is emerging that concomitant aspects of linguistic performance relate to the construction of particular sociolinguistic identities relevant to the medium, or, to adopt a less radical perspective, that sociolinguistic identities typical of face-to-face or written interaction are mediated by the social/communicative practices and norms relevant to, or accruing to, types of CMD. Language alternation features prominently among the mechanisms used in constructing such novel linguistic/social-performative identities. In this context, the research presented in this paper examines the performance of a group of six native speakers of Greek, who are also part of a relatively closely-knit social network. The analysis reveals extensive code-switching between Greek and English, both inter- and intra-sentential, with English covering around 20% of the total of words used. The qualitative analysis shows that expressions of affect and evaluative comments are mostly in English, while Greek is reserved for the transmission of factual/referential information. The data further reveal that extensive style- or register-shifting and mixing is a favored strategy among members of the group; such mixing includes shifting among dialects or sociolects of Greek, the use of other languages, and, notably, the use of constructed words and structures with humorous overtones. This complex type of language play is an overarching feature of the group’s (socio)linguistic performance in asynchronous electronic communication, which may single them out as a localized community of practice. The data highlight the theoretical and methodological necessity for fine-grained accounts of specific types of CMD, which can be tackled not in terms of overarching macro-contextual linguistic and extralinguistic variables, but as dynamic reflexes both of specific participant constellations and of the negotiation of emerging generic norms within localized communities of practice. The paper also presents and discusses a quantitative study of views and attitudes on language alternation expressed by subjects who code-switch systematically on email, in an attempt to gauge the types of metalinguistic awareness involved. It emerges from the quantitative study that users abstract away from ‘phobic’ attitudes towards the use of English and that they treat language alternation as a manifestation of balanced or functional bilingualism, which is furthermore situation-specific and ‘genre’-appropriate.