redirecting email to spam

[#1]

We have several email accounts.

In two cases the accounts receive unwanted emails where the sender has hacked somebody else's account and used the account to target me/ my family with some dubious threats. The apparent "sender" is always different so is difficult to block

Is there a way of re-routing the unwanted emails (by keyword search of the subject) to the spam folder?

TIA

[#2]

This depends on the client you are using. If it can do message filtering using information from a hesder field and you are using IMAP so uploading is possible you can copy spam messages from Inbox to the Spam folder on the server. I do that routinely using Thunderbird.