How to Delete Mail in Horde Webmail
Deleting Messages is a 2-steps process in Horde Webmail:
By default, in the Plesk-hosted Horde Webmail any messages deleted will be marked or moved to the Trash but not permanently deleted from the server. This means that when an email is deleted it continues taking up space.
Here is how to modify this setting so that deleted messages are placed in the Trash automatically:
1- Log into your Horde Webmail.
Usually the URL is: http://webmail.yourdomain.tld
Replace "yourdomain.tld" with your real domain name.
2- Once you have logged in, click on the Options button at the top of the page.
3- At the top right of the "Options" page, in the dropdown menu select Mail.
4- Next, under "Message Options" select Deleting and Moving Message.
5- Check the box next to "When deleting messages, move them to your Trash folder instead of marking them as deleted?":
6- Click on Save Options. Now any mail that you delete from your inbox will automatically go to your Trash folder.
7- You can then click the Empty Trash icon to permanently delete the emails.