Sorry that currently there are no effective way to use the junk or rules to delete all the messages in one click.
However, Kutools for Outlook's Block Sender Domins
provides a workaround: You can select all the spam mails, then right-click on any mail, select Junk (Kutools)
, then click Block Sender Domins
. Remember, if most of the mail domins are normal ones like gmail, you should select Block Senders
By doing so, all the emails you selected would be deleted, and future emails sent by these domins/senders will be blocked.
If you have any further questions, please don't hesitate to ask me.