The Horde webmail client has this strange default whereby messages are struck through instead of being deleted. This can be really annoying and confusing to a lot of clients.
Here is the solution to that problem:
1. Log in to Horde.
2. Highlight on the gear icon at the top of the page, located to the right-hand side of Notes.
3. Select Preferences, followed by Mail. This will open the Preferences for Mail page.
4. Under the Message column, select Deleting and Moving Messages.
5. Place a tick in the box labelled Move deleted messages to your Trash mailbox instead of marking them as deleted in the current mailbox?.
6. Click on the Save button.