It is possible by using QuickR Connector inside Lotus Notes, and the .eml file is shown inside LN. This connector will associate .eml files with LN as viewer. It helps to launch eml files outside of LN, it will launch Ln as to view .eml files. And now, LN acts as a viewer for .eml files.
Of-course, there are some 3rd party SW for the same purpose!