vpopmail and courier-imap

[Miranda Gomez Miguel Angel]

I have a question,
when i login into my webmail ( using squirrelmail and courrier-imap ) i can
read the email, after that i connect using my outlook and there is no
problem, but when i reconnect to the webmail i still can read the emails i
downloaded with the outlook , is this normal ??
i have to delete with the webmail all the emails to clean up the account (
and the space ), doesn't the pop protocol do this automatically ??
thanks