Good
"Valid emails are being deleted and as far as I can see they are not necessarily bounced back to the originator."
Well that's good. Having identified something as spam (even if wrongly), it would be cretinous to bounce it "back" to the apparent sender. Rule 1: spammers lie. I've had quite enough of other people's spam shovelled into my mailbox by MTAs configured by morons, thanks.
-A.