Sympatico and Apple Mail

I am a new Mac user (previously windows) and have just set up my email server (sympatico) to forward my email to my Apple Mail. I will be using this account for all my email actions. The only problem is that if I access my email remotely using www.getmail.sympatico.ca, ALL of my emails are there (the ones that I've already received in my Apple Mail. Does anyone know why this is happening and how I can fix this? Thank you!