In this paper, we proposed and developed a new function that can spread E-mail use based on reliable X.400 protocol. This function, we named EMSS(Electronic Mail Support System), provides following three characteristics. The first one is to use line mode operations in all terminals. The second is to retrieve the mail address for personal use in the mail server. The third is to specify conditions to receive mails to shorten the connection time in the mobile environment. As a result of having supplied EMSS to a real operating environment, the number of terminals with no support X.400 protocol begins to occupy 24%. Furthermore, even if the use in a mobile environment increased in 2.0-2.5 times, increase in communication costs were restrained among 1.3 to 1.7 times. This effect is an example in our site, however we achieved our original aim that is the spreading E-mail use.