The purpose of this study is to identify and assess the key elements and the effectiveness factors of CRM. In this study some cases such as the relationship between key elements of CRM and effectiveness factors of CRM and its dimentions (market and customer performance, internal organization performance) was examined. Besides, the degree of anticipation of CRM eight elements (TMA, CM, culture and organization, CRM strategy, IT, people, KM and processes) in relation with the CRM effectiveness was taken into consideration. Finally, the role of effectiveness of sex, education level and employment status on CRM effectiveness in Shiraz post offices was examined. The result of the present research was access to the eight key elements of CRM in Shiraz post offices (i.e. TMA, CM, culture and organization, CRM strategy, IT, people, KM and processes). Correlation between key elements and effectiveness factors was confirmed. According to the nature of post administration, the research findings recommended that "KM" played the most important role in effectiveness and after that TMA, CM and finally IT took the next ranks. In other findings, we came to this conclusion that there was not a meaningful correlation between the nature of sex, education level and employment status and the effectiveness of CRM.