Post fix mail duplicate download issue

hi,

i'm having a post fix email server and clients are accessing with out client. Once client accessing email from LAN and from his Broad Band connection too. Once that user download mails from server on LAN, when he try to access the emails again from home using his Broad Band connection same email again download to his .pst file. tried several ways still issue is there. please support me.

Clients are accessing without client?

Users do not download mail from Postfix, you need some other software for that.