The spam quarantine folder can be access via either webmail or IMAP.
Follow these steps to access your account’s spam quarantine folder using webmail:
Step One: Login at https://mail.psmail.net/
Step Two: Click on PSMailbox, the menu will open to sub-menu items
Step Three: Click on Quarantine in the sub-meny to open the SPAM quarantined folder.
In the Legacy webmail window:
When you are logged in , click on the icon that looks like Trash/Recycle Bin 
OR
Click on Folders and at the bottom of your folders list, click on the TRASH FOLDER link.
Follow these steps if you want to access your spam quarantine emails using IMAP:
Step One: Open your email client.
Step Two: Explore IMAP folders (this will vary for each IMAP email client)
Step Three: Expand PSMail/quarantine to find a folder called “deleted”
Step Four: Open the folder PSMail/quarantine/deleted