No law can forbid you from marking an email as SPAM
There are several spammers who think that by quoting an unknown law then you won’t have the right to mark their email as SPAM. They’re clearly making a mistake, but you don’t have to argue with them. If you consider that your mailbox has emails with undesired content, then you should mark them as spam before you start deleting. There are no law that can ever forbid you for doing what you want with the received emails, except for the one in which you are not allowed to publish personal information about the sender. The rest is up to you.