iCloud emails disappearing into the clouds

Hi, I’m not receiving all of my iCloud emails, for example I purchased e tickets for an attraction, but nothing came through to my iCloud, if I register on a new site, I don’t receive confirmation emails, they don’t go to junk/trash or archive. I checked email settings and nothing has changed. This has been happening from around January time. I have been using my BT email for new sites since then, but recently forgot and used my iCloud email for the e tickets mentioned above