In Webmail there is sometimes only a “select all” option then “delete” and it is difficult to do housekeeping, especially with Zen
However here is a much better when you also use Outlook
Go into the “Account settings”, click “change” and click “more options” (might be “advanced” on some versions of MS Outlook)
Click on “leave a copy on the server”, this then gives you 2 further options “delete from server after ?? days”
Or
“delete from server when removed from deleted items”
Using one or both of these options will keep webmail nice and tidy