Here's another suggestion for combating the spam we are getting at the moment (Feb 2021). Hopefully it won't be needed once the built in spam filter is working again.
To set it up:
If you want to check how well this will work before trying it, you can view the source of a few incoming emails:
Below 'Authentication-Results' you see most legit emails say 'spf=pass' while most spam won't.
SPF is a protocol that was introduced to reduce spam, so it works quite well.