s 210 then a mailing address is written to the mailing field of the electronic mail in step s 220 thereafter the automatic checking procedure of the mail sending software is initiated by point clicking a button in the mail sending software in step s 230 hence the mailing addresses in the mailing fields are automatically checked to determine whether they are among the previously set predetermined mailing addresses in step s 240 if the mailing address is included in the predetermined mailing addresses the mailing address is preserved without any changes on the other hand if the mailing address is not included in the predetermined mailing addresses the mailing address not included in the predetermined mailing addresses is specially highlighted through the mail sending software in step s 250 the method of specially highlighting the mailing addresses to the user includes reversing the foreground color and the background color of the batch of mailing addresses or changing the font size and or color of the mailing addresses however this should by no means limit the scope of the present invention in general the user may choose some other special highlighting method and yet still be considered within the spirit of the present invention if the mailing address is one among the previously set predetermined mailing addresses or the mail sending software has.