The aim of this study was to determine the extent to which the linguistic signs used by adolescents in electronic mail (email) differ from those used in traditional written language. The study was conducted in French, a language with a deep orthography that has strict, addressee-dependent rules for using second person personal pronouns (unfamiliar and familiar forms). Data was collected from 80 adolescents ages 12 to 15 in a natural situation where they had to introduce themselves by email to two addressees, a same-age peer and a teacher. The adolescents were divided into two groups (expert / non-expert) according to their expertise in computer-mediated communication. The results showed that for adolescents, email constitutes a written-language register of its own. Moreover, in terms of adaptation to the addressee (pronoun use), the email register seems to follow the pragmatic rules of traditional spoken and written interaction. The observed differences between the CMC experts and non-experts suggest that the email communication register is acquired gradually.