but now, i am thinking that this solution may not be appropriate, because a user at my server may has username here as A but his pop3 email account may be abraham@tm.net.my. this will bring problem for me when i want to use procmail to filter the receipeint name and put the email into correct mailbox.

Fetchmail does already support the specification of different usernames and passwords (from that of the local user account) for remote mail servers. Differing local user accounts can be specified within fetchmailrc files through the here directive - For example:

poll mail.remotehost.com protocol pop3 port 110
    user "user@remotehost.com" with pass "password" is "me@localhost" 
+here
[download]

by the way, if i want to write a script to retrieve pop3 emails for multiple users, what modules can i use?

There are a multitude of modules available - The following are those which I think merit your attention primarily:

• Mail::Audit,
• Mail::Procmail, and
• Mail::POP3Client (or Mail::IMAPClient)

Of these modules, Mail::Audit will be of the most interest to you from the perspective of the handling, filtering and delivery of mail messages - This module is very well documented and there is also an excellent introductory article for this module in Issue 18 of The Perl Journal here.

The Mail::POP3Client and Mail::IMAPClient modules will be of use in the retrieval of messages from external mail servers via POP3 and IMAP4 respectively.