I can not delete the messages/move them into the trash. What do I have to do?
The reason you could not delete the emails has been caused by the selected option to move deleted emails into the trash folders. This option requires a copy task which can not be executed when the account is over quota. To get out of this situation you have to change your settings (do not select the option “move email to trash folder”). After this, you will have to make more space in your mailbox by deleting (and purging) additional messages, not just in your Inbox but also in any other folders.