Encryption is used to convert an email message to an unreadable format thereby securing patient privacy during the transmission of the message across the Internet. Two available means of encryption are: public key infrastructure (PKI) used in conjunction with ordinary email and secure hypertext transfer protocol (HTTPS) used by secure web-mail applications. Both of these approaches have advantages and disadvantages in terms of viability, cost, usability and compliance. The aim of this study was develop an instrument to identify the most appropriate means of encrypting email communication for telemedicine. A multi-method approach was used to construct the instrument. Technical assessment and existing bodies of knowledge regarding the utility of PKI were analyzed, along with survey results from users of Queensland Health's Child and Youth Mental Health Service secure web-mail service. The resultant decision support model identified that the following conditions affect the choice of encryption technology: correspondent's risk perception, correspondent's identification to the security afforded by encryption, email-client used by correspondents, the tolerance to human error and the availability of technical resources. A decision support model is presented as a flow chart to identify the most appropriate encryption for a specific email-based telemedicine service.