A structured analysis of peer-reviewed literature about the delivery of health services by email was undertaken for this review. A total of 185 articles were included in the analysis. These articles were thematically categorised for medical specialty, participants, sub-topic, study design and service-delivery application. It was shown that email-based telemedicine can be practiced in a large number of medical specialties and has application in primary consultation, second opinion consultation, telediagnosis and administrative roles (e.g. e-referral). Email has niche applications in low-bandwidth, image-based specialties (e.g. dermatology, pathology, wound care and ophthalmology) where attached digital camera images were used for telediagnosis. Diagnostic accuracy of these images was the predominant topic of research and results show email as a valid means of delivering these medical services. Email is also often used in general practice as an adjunct for face-to-face consultation. Further, a number of organisations have significantly improved the efficiency of their outpatient services when using email as a triage or e-referral system. Email-based telemedicine provides specialist medical opinion in the majority of reviewed services and is most likely to be instigated by the patient's primary care giver. However, email-consultations between patient and primary care and patient and secondary care are not uncommon. Most email services are implemented using ordinary email. However, a number of organisations have developed purpose-written email applications to support their telemedicine service due to impediments of using ordinary email. These impediments include lack of management tools for: the allocation and auditing of cases for a timely response and the co-ordination of effort in a multi-clinician, multi-disciplinary service. The ability to encrypt ordinary email thereby securing patient confidentiality is also regarded as difficult when using ordinary email. Hence, alternative web-based email applications where the encryption can be implemented using the more user-friendly HTTPS have become popular. Much of the reviewed literature is descriptive or anecdotal and hence, suffers from lack of conclusive results regarding positive patient outcomes. This may account for email-based telemedicine generally being regarded as underutilised. However, the potential is well recognised.