Here is the command to mass delete a message from a Dovecot mailbox:
doveadm expunge -u existing-user@existing-domain.com mailbox Inbox FROM bad-actor@domain.example.com
Here is the command to mass delete a message from a Dovecot mailbox:
doveadm expunge -u existing-user@existing-domain.com mailbox Inbox FROM bad-actor@domain.example.com