If your spam folder is not on the list in squirrelmail, these
instructions show you how to put it there. :)
First, log into squirrelmail:

Once logged in, click on the "Folders" link on the top of the
screen. Then you'll go here:

In the photo above, I've scrolled to the bottom of the page.
Click on the folder "SPAM" and then click the subscribe button.

When you do that, it will move to the left (I've scrolled to the bottom
of the page again in the photo). Now, you are subscribed.
To refresh your folder list on the left, you can either log out and log
back in, OR you can click on the link "Refresh Folder List" at the top
of this page.

If you click that, you'll see the spam folder on the left. You
can now open it to look for spam. (You'll find a TON of spam that
has been filtered. It's safe do delete anything in there, but
make sure to check for wrongly identified stuff.

Hope that helps!!!