To delete emails in the e-inbox folder or to empty folders, open and do the following:

1. Open your account and click on "Mail".
2. Click on "Select" under "Selection". After that, a box will appear in front of each email, which is also convenient for further email editing.

Email selection option with box in front of it:

To completely delete content in any folder, select the folder and then select "Empty" under "ThreePoint Menu".

After that you will be asked again, "Do you really want to delete all messages in this folder?" and with "Delete" the folder will be emptied (contents irrevocably deleted).