imap_delete not working

I am using php imap functions to parse the message from webmail. I can fetch messages one by one and save them in DB. After saving, I want to delete the inbox message. imap_delete function is not working here. My code is like that:

$connection = pop3_login($host,$port,$user,$pass,$folder="INBOX",$ssl=false);//connect
$stat = pop3_list($connection);//list messages

foreach($stat as $line) {
  //save in db codes...
  imap_delete($connection, $line['msgno']);//flag as delete
}

imap_close($connection, CL_EXPUNGE);

I also tested - imap_expunge($connection);
But it is not working. The messages are not deleted. Please help me out...