Hi, apparently my MUSS has reached 90% capacity and in order to receive e-mail through the account, I have to erase the past e-mails.
There was this "deleted" button with "set" and "clear" beside it but when I press that, an envelope icon beside the e-mail has a red x across it but it doesn't get deleted (and thus the capacity does not open up).
How do I permanently delete e-mails from MUSS?
Thanks in advance!

There's a button near the bottom that says "Purge Deleted"
It will get rid of any email that is marked as deleted with the little red "x"