Accessing the SPAM folder

I'm in the process of writing a basic开发者_StackOverflow社区 PHP email client. So far I've written a basic POP3 class using fsockopen. It works great so far however I'm noticing a big limitation. The POP3 protocol doesn't have support for folders, which means I can't access the SPAM folder. How do hotmail and yahoo's clients access the SPAM folder? Do they store it on a different non-POP3 server?

I find the SPAM folder is important to include in the client as some undeserving emails end up there.

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POP3 doesn't have a concept of folders. It's there to access what amounts to your Inbox only. For folders, you need to use IMAP.