[ALUG] Thunderbird problem OT?

I have googled this but haven't yet found anything that addresses the problem I have. Every so often I'll get emails that are directed to the spam folder. Some will be spam, but some are emails I'd like to know about. The difficulty is, I don't know there are any in the folder unless I look because, unlike other folders, it doesn't show a number for new emails. I've put the addresses into my address book, I've made sure I have subscribed to the folder. Nothing's worked so far. Any ideas? Bev. (Linux Mint 19.01., Thunderbird 68.4.1)