can i unsync mail and btyahoo

I have a btinternet account which I check on the web page btyahoo as well sometimes. If I delete from the web site it also deletes from my inbox on the mac mail too 😟 how the **** do I stop this?? At present I dare not delete anything other than spam from the web page in fear of losing important mail at home - I'm sure i must have clicked something but it sure needs unclicking lol

Thanks

MD