Mobile email is one of the first widely accepted mobile business application in enterprise settings that can be used by mobile phones. In this paper, a study about the role of mobile email as a performance driver in the everyday knowledge work of different business users in multinational information and communications technology enterprise is presented. Everyday communication task contents and volumes of knowledge workers were identified and analyzed by interviews, communication task diaries, and survey to understand the communication task goals and patterns of typical knowledge workers in enterprise settings. The study reveals that the biggest share of the knowledge workers' overall businessrelated communication (regardless of the communication tool and application) is centered on the internal communication tasks, and respectively, mobile email is used most intensively in the internal communications tasks. When comparing the relative importance of mobile email as communication solution for business users in different work positions, the study shows that mobile email is the particularly important everyday performance driver for managers who travel a lot and whose communication volumes in overall are extensive because of their role as central activity progress enabler for other work communities. Intensive users of mobile email gain more personal benefits than non-intensive users. The importance of mobile email is only moderate in the everyday business communication of those who are not in managerial positions. This implicates that mobile email as a business performance driver should be understood and evaluated by corresponding it with the internal process performance objectives and measures.