Does not erase messages on server

[Robert Eisig <quantumchaos666@xxxxxxx>]

Hi,

I am on win32 using the mutt native port (no cygwin).

When I download new Messages with "G", mutt asks my if received messages 
on the server should be erased, I answer yes.

But they are not erased. So each time I get duplicates from old 
messages. Over and over again, imagine my inbox ;-)

1) how can I achieve that downloaded messages are really erased?

2) how can I achieve that downloaded messages are erased after x days?

3) how can I achieve that already downloaded messages are not downloaded 
again?

Should I use a different program to fill my inbox? My inbox is a local 
File, type unix-mailbox.

My version is mutt-1.4 (win32) by Ulf Erikson,
http://www.geocities.com/win32mutt/

Thank you for any help!
Robert