It's more likely the spam filtering already happened on your email provider's server. You can try to login to your account via webmail and fix things on the server. If in doubt, ask your email provider.

There is no spam filtering on my providers server that I can find.

Who is you provider? Is your account IMAP or POP?

Matt - it is possible that you are right. When I log into 1&1 to configure my emails there is no option for spam filtering. However 1&1 is now Ionos - when I try to log in here my password isn't accepted, and nothing else works - it seems from the ads that there is spam filtering here. I am trying to sort this out with Ionos at the moment. (Don't know why they keep the old out of date 1&1 page going). Stay tuned.

See https://www.ionos.com/help/email/setting-up-mail-business/activate-or-deactivate-anti-spam-for-your-company-name-email-address/

Hi Matt, Yes I tried that, but I couldn't get in to Ionos - even though they have a page for taking your 1&1 password over! After a long chat with Ionos I finally found out that they have separated back again from 1&1 last November (didn't tell me!) - so I'm back to the 1&1 again. Haven't got any further yet.... Must try by 1&1 again sometime. Gordon