>I do, and it is always empty, but for a message telling me that spam was junked.
So maybe previous HMRC, paypal, bank phishing etc emails have been going to your spam folder (which then must quickly delete them) so this latest HMRC will be one that slipped through the net. And maybe emails from your son at work are still bypassing your in box.
Or maybe you have just been very careful with giving out your email address. After getting loads of spam I opened a new email address 3 months ago and have used it carefully, leaving my older addresses for less trustworthy contacts. The only entries in the spam box are, erm, the AnswerBank Newsletter