Please share what you have attempted? For example, I can highlight a large number, rightclick and delete. Knowing what you have tried will help. The Edit>Find>search lets you locate mail for a timeframe, and then select and delete. Tell us more.

Thank you for your answer. What I tried was what worked with my Deleted box: highlight the whole list and click "Delete". But, when I tried this with the Inbox, it didn't work. So I've just tried your suggestion. But I'm afraid that I got the same result: it'll work when I highlight only three or four but not when I try to delete a whole bunch. Do you know why that might be so? Best wishes - SW

I would log onto the account via web interface. Thunderbird could probably do this, but to get it done, I would go to the source.