Significant research work has been conducted in the area of process mining leading to mature solutions for discovering knowledge from structured process event logs analysis. Recently, there were several initiatives to extend the scope of these analysis to consider heterogeneous and unstructured data sources. More precisely, email analysis has attracted much attention as emailing system is considered as the principal channel to support the execution of business processes. However, existing initiatives didn’t formalize the relationship between emailing systems and business process elements. As a result, they target to discover business processes limited to the activity perspective. In this paper, we first propose a meta model to specify what kind of process knowledge we can discover from emails. We define by this way a research roadmap for an effective multi-perspective process discovery from emails. This metamodel is proved through a concrete case study related to "hiring", "patent application", and "paper submission" business processes. In addition, we highlight the limitations of current process mining techniques in the discovery of different process perspectives.