Doubt about poppassd working togheter vpoppmail

[70210@bol.com.br]

My e-mail solution is: RedHat 7.2, qmail, imp and vpopmail.

My poppassd is working .I can change passwords that are located in
/etc/passwd trough telnet myserver 106

I access imp webpage and log into.
When I try change my password I recive a message: "500 Old password is
incorrect "  but I have 100% of sure that my old password is correct.

I have a simple doubt, but fot me it is huge now . Poppassd can work with
virtual domains that were created using vpopmail? How can i do it?

My best regards
tks for all